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Notes: To understand the density-gradient expansion approximation for the exchange-correlation energy of density-functional theory from a fundamental viewpoint, we have performed an analysis of the corresponding expansion of the Fermi-coulomb hole charge distribution. The Fermi-Coulomb hole represents the correlations between electrons resulting from the Pauli exclusion principle and Coulomb's law. The analysis is performed in the exchange-only approximation by considering the expansion for the Fermi hole to terms of O(▽3) as applied to atoms. Our study shows that the expansions to O(▽), O(▽2), and O(▽3) all severely violate the constraint of positivity, becoming progressively worse with increasing orders of ▽. Further, the expansion to O(▽2) also severely violates the constraint of charge neutrality. (Terms of O(▽) and O(▽3) do not contribute to this constraint or to the exchange energy.) Thus the description of the physics of Pauli correlations in atoms as given by this approximation is highly unphysical. In spite of this, the exchange energy to O(▽2) is superior to the local density approximation because the expansion hole better approximates the exact Fermi hole in the interior of atoms from which arise the principal contributions to the energy. However, the improvement is not substantial, as the oscillations in the expansion Fermi hole occur within the atom itself. For asymptotic positions of the electron, the expansion holes to each order neither approximate the local density approximation nor the exact Fermi hole. Thus we understand why the expansion cannot lead to accurate highest occupied eigenvalues. The oscillations of the expansion Fermi hole also demonstrate why the Slater potential and electric field that result from these hole charge distributions are singular. On the other hand, we show that the expansion approximation is mathematically consistent in that the coefficient of the gradient correction term for screened Coulomb interaction to O(▽2) as obtained from the approximate Fermi hole is the same as that derived from linear response theory. We conclude with remarks on the Coulomb hole as obtained within this gradient expansion approximation scheme.

Notes: The functionals adopted in the present work are those of DePristo and Kress [Phys. Rev. A35, 438 (1987)] for the kinetic energy, of Cedillo et al. [Phys. Rev. A38, 1697 (1988)] for the exchange energy, and of Wilson and Levy [Phys. Rev. B41, 12930 (1990)] for the correlation energy. In addition to the kinetic-, exchange-, and correlation-energy functionals, the total-energy functional used in the present calculations contains also the functional describing the interaction of the electrons with the atomic nucleus, and the functional describing the classical or direct part of the interaction among the electrons. Using these functionals, a two-parameter and a three-parameter variational density-functional calculation of the total atomic binding energy of the Ne atom is carried out. The electron (number) density of the Ne atom is modeled by using hydrogenlike one-electron radial wavefunctions (with the 2s radial function orthogonalized to the 1s radial function) containing two/three variational parameters. It is found that the calculated correlation energies are in reasonable agreement with the correlation energy value obtained from the Wilson and Levy expression with a Hartree-Fock electron density.

Notes: The molecular and electronic structures of ADPO 1, a model thiapentalene 2, and [Xe2F3]+ have been calculated in the local-density functional (LDF) formalism with polarized double numerical basis sets. The molecules were calculated to have planar C2ν structures in agreement with experiment and in contrast to Hartree-Fock molecular-orbital calculations. The vibrational spectra of all species were calculated to show that the optimized structures are indeed minima. The calculated spectrum of [Xe2F3]+ is compared with the experimental one and excellent agreement is found. These results demonstrate that the LDF method can be applied to the prediction of molecular structures containing hypervalent bonds.

Notes: Molecular dynamics simulation of mixed quantum-classical systems, in situations where the quantal degrees of freedom undergo transitions among states, poses a number of challenging problems. Among the difficulties are bifurcation of trajectories that evolve into different quantum states and proper treatment of quantum coherence. In this article we outline the problems and contrast the ways in which they are addressed by current methods for nonadiabatic molecular dynamics. In the course of this comparison we present a new result, the relationship between the velocity adjustment in the “surface hopping” method and the “Pechukas force,” as well as some new reflections on an old result, oscillatory yields in ion-surface scattering.

Notes: A density-functional theory describing the superconducting state of matter is presented. The formalism leads to a set of single-particle equations that are structurally similar to the Bogoliubov-de Gennes equations but (in contrast to the latter) incorporate both normal and superconducting exchange-correlation effects. It is demonstrated via a rigorous decoupling scheme that these single-particle equations are equivalent to a set of normal Kohn-Sham equations, and a BCS-type gap equation to be solved self-consistently with the Kohn-Sham equations.

Notes: Determining mechanisms of chemical reactions involves finding dynamical paths between desired (given) reactant and product states. We have developed a method that is based on recasting the principle of stationary action into a general and computationally tractable form that yields all dynamical paths connecting the initial and final configurations of the system. Thus the method has advantages over the traditional initial-value trajectory calculations for solving such boundary value problems. We give some examples of reaction paths for H(2S) + O2(3Σg-) ↔ OH(2II) + O(3P) on the ground state potential energy surfaces HO2(2A″).

Notes: Electrostatic solvation energies of singly charged monoatomic ions may be predicted from the knowledge of an electrostatic potential buildup from a physically meaningful ionic radius. Since the asymptotic behavior of the electrostatic potential for cations and anions do not follow the same pattern, different methodologies are needed. The reaction field potential required for the calculation of Born's solvation energies of singly charged cations may be obtained from the simple Thomas-Fermi-Dirac theory, based on the condition that the electrostatic potential of the ground-state atomic ions do exactly equal the negative of their chemical potentials. For singly charged anions, electrostatic solvation energies may be directly obtained from Sen-Politzer electrostatic potentials. Numerical results are presented for two representative series of ions and compared with experimental data.

Notes: The electrophilic substitution in a series of 5-aminobenzofurans was investigated by all-valence electron AM1 molecular orbital calculations. Various molecular properties of the reactants, intermediates, and products were computed and compared with available experimental data. The results indicate that while calculated ground-state charge densities cannot be used to predict reactivity and orientations, the relative thermodynamic stabilities of the reaction intermediates (arenium ions, σ complexes) reflected by calculated heats of formation (ΔHƒ) accurately indicated the isomers resulting from the kinetically controlled substitutions. The relative stabilities of the reaction products could be used to predict reaction preferences for the thermodynamically controlled electrophilic substitutions. Positions 4 for both aniline and 5-aminobenzofurans were the most susceptible toward electrophilic attack. The calculated ΔHƒ of the reaction intermediates, in good agreement with the experimental data, were capable of distinguishing between slightly nonequivalent positions such as the ortho and ortho prime to a substituent. Calculated AM1 ΔHƒ may represent practical guides in the prediction of sites of electrophilic aromatic substitutions for molecules with complex structures.

Notes: We have performed ab initio (3-21 G) calculations on the weakly bound donor-acceptor complex between benzene and tetracyanoethylene (TCNE) as a function of various intermolecular motions. The resultant potential energy surface (PES) was then fit to the product of analytical functions. Classical dynamics was performed on this PES by solving Hamilton's equations using a fourth-order Runge Kutta differential equation solver. Time steps were of the order of 1.0 femtosecond and the system was allowed to evolve for 1,000,000 time steps. Fast Fourier analysis of the resulting trajectories indicate that the primary intermolecular vibrational frequencies are 118, 228, and 232 cm-1. These correspond to the motion of the intermolecular separation coordinate, and the two twisting coordinates. We also discuss other possible solutions, zero-point energies, etc.

Notes: Some of the fundamental theoretical concepts for molecules in homogeneous strong magnetic fields are discussed. First, we perform the pseudoseparation of the center of mass motion for neutral as well as charged systems. The resulting Hamiltonian allows us to investigate the problem of the Born-Oppenheimer adiabatic separation of electronic and nuclear motion in the presence of a magnetic field. In particular, we study the most important differences to the field-free case. Finally we discuss the symmetry groups for molecules in a magnetic field and investigate the possibilities and effects of the interaction of molecular electronic states through nuclear motion. Even for diatomic molecules severely enhanced nonadiabatic effects may occur in a magnetic field.

Notes: In this work we analyze the interrelations between potential energy changes and molecular shape changes along the reaction paths for a series of ring-opening reactions. The processes studied correspond to the opening of the four-member rings of 1,2-dioxete, 2H-oxete, 2H-thiete, and 1,2-dithiete, which recently have been given considerable attention in the literature. We describe the molecular shape in terms of a continuum of fused-sphere surfaces, which are characterized by using molecular topological methods. The four processes cover a range of reaction enthalpies from largely exothermic to almost thermoneutral. The similarity between the configurations found along the reaction path is assessed quantitatively in terms of parameters associated with the molecular shape and the path itself. We find a correlation between the value of the energy barriers (and reaction enthalpies) and the similarity parameters. The correlation is comparable to that found in the case of various other processes, such as torsional changes, collisions, and intramolecular atom displacements or shifts. The results are in line with the intuitive correlations expected from the Hammond postulate.

Notes: A general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.

Notes: The study of atoms and ions in unusual environments is an area of current interest. Examples of such environments are the Crab pulsar, where magnetic fields well in excess of 1012 G are encountered and plasmas, studied under intense laser irradiation, where “confined” atoms are subjected to electric fields corresponding to laser fluxes of 1018 W/m2. In this article, a unified theoretical approach is presented to treat atoms in such intense fields. The major theoretical tool employed is the Bloch or canonical density matrix. This is used first for treating magnetic fields, numerical examples of heavy atoms, and ions in intense fields being referred to specifically. Then the same theory is used for “confined” atoms in intense electric fields. Very brief reference is made to molecules in magnetic fiels, with the illustrative example of the simplest molecular ion H2+.

Notes: We employ a method for solving the time-dependent Schrödinger equation for an atom or molecule in an intense, pulsed-laser field to study multiphoton emission processes. Single-electron effective potentials have been developed that reduce the computational effort required for multielectron systems. Illustrative results for electron and photon emission rates from krypton at 532 nm in the intensity range (1-4) × 1013 W/cm2 are presented and compared to recent measurements.

Notes: We studied the influence of the additives of tetracyanoethylene (TCE) (radical-anion acceptor) and the variations in exciplex concentration on the magnitude of time-resolved magnetic field effect in a delayed excimer fluorescence in polar exciplex system pyrene-N,N-diethylaniline. The nonmonotonous dependence of the magnetic field effect on tetracyanoethylene concentratration was found. The magnitude of the magnetic field effect was brought close to the predicted maximum limit of about 300 ns by decreasing the exciplex concentration. We conclude that the yield of the triplets, resulting from intercombination transitions in a singlet exciplex, is rather small. The upper limit for the rate constant of these transitions has been determined to be less than 4.6 × 106 s-1.

Notes: An orbital polarization (Hund's second rule) correction to local spin density (LSD) theory is developed in both a spherical harmonic basis and in a crystal field basis, and applied to the electronic band structure of FeO, CoO, NiO, and La2CuO4, resulting in a substantial enhancement of the LSD insulating band gap for NiO, and the creation of insulating band gaps for FeO, CoO, and La2CuO4.

Notes: Variational calculations have been carried out on the ammonia molecule using two-dimensional potential energy functions. The two dimensions used are the inversion and symmetrical stretching coordinates. If the potential function includes a term to describe the interaction between these two coordinates, the results are as good as those obtained in other studies using a six-dimensional potential function. The barrier height for the new potential function is 1857.5 cm-1.

Notes: Ab initio molecular-orbital calculations were carried out on carbon monoselenide (CSe), its cation CSe+, and the selenoformyl cation HCSe+. Equilibrium- and transition-state geometries on the potential energy surfaces (PES) were located at the HF and MP2 levels using a valence double-ζ (d, p) basis set on H and C and the Huzinaga valence triple-ζ (d) basis set on selenium, respectively. The global minimum on the HCSe+ (PES) is the linear species 3 with the dissociation energy towards H and CSe+ of 151.5 kcal mol-1 (MP4//MP2 + ZPE level). While at the HF level the strongly bent isomer 4 is a local minimum structure lying 67.8 kcal mol-1 above 3 and separated from 3 by a small barrier of 6.2 kcal mol-1, MP2 geometry optimizations suggest that CSeH+ isomer is unstable.

Notes: The UV photoelectron spectra of 2-halogenofurans, together with 3-iodo and 2,5-diiodofurans, have been studied. The assignment of the lower energy region of the spectra was based on correlation of the ring π- and halogen levels in the related compounds, resolved vibrational structure, and in case of 2- and 2,5-diiodofurans by considering the relative intensities of their He I/He II spectra.

Notes: Ab initio Hartree-Fock band structure calculations are presented for the first time for lithium phosphide (Li3P) and lithium arsenide (Li3As) in the hexagonal P6/mmm crystal structure. Results are compared to those for lithium nitride (Li3N). The new calculations for Li3N agree with previous Hartree-Fock calculations, except for the valence band structure where results of previous pseudopotential calculations are confirmed. Geometry optimization for Li3P yields a lattice parameter a of 4.45 Å and a c value of 4.80 Å. These values differ markedly from experimental results reported to be 4.271 and 7.590 Å, respectively. A similar discrepancy is found for lithium arsenide: a = 4.60 Å and c = 4.96 Å have to be compared to the reported experimental values of 4.397 Å for a and 7.824 Å for c. Force constants are derived for in-plane and interplane vibrations. The band structures for Li3P and Li3As are found to be very similar to the one calculated for Li3N. Using Li3P as an example, it is shown how the band structure of the insulator can be derived from the band structures of the two metallic constitutent Li2P and Li monolayers. The metal-insulator transition occurs if the inter-plane distance falls below 4.25 Å. Contrary to expectations raised earlier, it is found that the 3d electrons in arsenic are strongly localized, evidenced by a very narrow d band width of 0.1 eV. They cannot be used to explain the difference in conductivity between the phosphide and the arsenide. A Mulliken population analysis gives charge distributions close to the ideal ionic structure (Li+)3X3-, X = N, P, and As. Overall it is found that hexagonal lithium phosphide and lithium arsenide arsenide are more similar to lithium nitride and less anisotropic than suggested previously. This discrepancy could be due to the use of polycrystalline samples in earlier experiments.

Notes: The electronic structure of the polyhedral carboranes 1,5-dicarba-closo-pentaborane(5) and 1,5-dicarba-closo-pentaborane(3) is studied using ab initio calculations, and compared to that of their hydrocarbon analogs bicyclo[1.1.1]pentane and [1.1.1]propellane, respectively. The high symmetry and common topology of the carborane-hydrocarbon structural analogs force similar bonding patterns, and the carboranes show a unique three-center, two-electron CBC bond not previously observed in these species. This three-center bond is formally analogous to the σ-bridged-π bond in the hydrocarbons, but its strength is low and its C—C bond long. Analysis of the bonding in these carboranes along with that in 1,3-diborabicyclo[1.1.1]pentane, another[1.1.1]propellane analog, shows that the strength of their three-center bonds is directly related to the nature of the bridging group, but is independent of the type of bridgehead atom. 1,3-Diboretene, the carborane analog of bicyclo[1.1.0]butane, is also found to exhibit a similar bonding pattern to its hydrocarbon analog and to possess a CBC bond.

Notes: Ab initio calculations of the molecular geometry and electronic structure properties (charges, dipole moment, polarizability, HOMO and LUMO energies) of acrylonitrile, CH2=CH—C≡N, cis- and trans-2-butenenitrile, CH3—CH=CH—C≡N, 3-butenenitrile, CH2=CH—CH2—C≡N, and 2-methyl-2-propenenitrile, CH2=C(CH3)—C≡N are obtained at the 3-21G level. Results on three anionic derivatives of these molecules obtained at the 3-21+G level are also reported. Properties of the molecules in their isolated states are considered as a preliminary basis to compare initial steps of bulk and surface polymerization of vinylic monomers by electrochemistry under cathodic polarization.

Notes: Elucidating, from a molecular point of view, the differences and similarities in the properties and reactivity of matter in the gaseous compared to the condensed state is a subject of considerable current interest. Although there are a number of promising approaches to this problem, one of the alternatives involves the use of clusters that enable detailed spectroscopy and reactivity investigations to be accomplished as a function of degree of solvation under well controlled conditions. New insight into a variety of phenomena of interest in liquids have been derived from recent studies in our laboratory. In particular, the findings have contributed to unraveling the reactions of ionized functional groups in organic molecules that are influenced by solvation effects, identifying the structure of protonated complexes among species of varying proton affinities, and quantifying the variations in spectroscopic properties of chromophores as influenced by solvation and aggregation. Various examples from the author's laboratory are discussed, including solvation-driven reactions as well as alcohol and acetone dehydration reactions, the influence of clustering on the reaction of OH- with CO2, structures of protonated species comprised of water, ammonia, and trimethylamine; also presented are the results of studies of the influence of solvation on the absorption of photons in the chromophore of tyrosine, namely phenol.

Notes: A study of the electronic structure and spectroscopy of models of C60 and C70 cage structures has been carried out using the intermediate neglect of differential overlap (INDO) model Hamiltonian. The geometry for these cages was obtained using gradient-driven methods, and at least in the case of C60, where information is available, is in good accord with the calculations of others. Using a small active space of only single excitations, both configuration interaction (CI) and random phase approximations (RPA) yield spectra in excellent agreement with that obtained from recent experiments. The oscillator strength of the band calculated at ∼47000 cm-1, however, dramatically diminishes as the active space is increased, even though the sum rule increases. We discuss this interesting observation as well as the calculated structure and spectrum of C70.

Notes: We examine the inclusion of spin-orbit effects within the Rumer configuration interaction technique and discuss its implementation in the spectroscopic version of the intermediate neglect of differential overlap model (INDO/S-CI). An efficient strategy for calculating excitation energies, transition moments, and Mulliken populations for Rumer-adapted functions is described. As an example, results are presented for the ground and excited states of the hydrated trivalent cerium ion [Ce(H2O)9]3+, which confirm the low energy assignments to 4ƒ → 5 d transitions split by some 10000 cm-1 through spin-orbit coupling and ligand field interaction. Comparisons are made between this technique and one that we have used previously that utilizes configuration interaction over double-group adapted linear combinations of determinants.

Notes: The angular and energy dependence of minima of the differential scattering cross section (DCS) for electrons scattered elastically by selected target atoms is studied using the nonrelativistic Hartree-Fock wavefunction for the static field and local energy-dependent function for the exchange and polarization potentials for the target atoms. The parameters contained in the polarization potential are varied to determine the minima of the DCS with respect to the scattering angle and incident energy with the constraint that the integral cross section agrees with the experimental value within the uncertainty of 5% at a selected energy. The resulting effective interaction potential is then used to compute the DCS over the intermediate energy range for the target atoms. The computed values are in good agreement with recently published experimental and theoretical cross section for helium and neon atoms.

Notes: Using computational SCF and MCSCF followed by extensive variational and perturbational CI calculations, we study the insertion routes of a copper atom into the carbon-hydrogen bond of a methane molecule. Here we show the importance of the initial reaction routes of the interaction for obtaining the final products of maximal probability. Because of the initial conditions of this reaction, our study shows that not all of the HCuCH3 intermediate complex dissociation channels in Part I can be easily reached. Another important result presented is the nonlinearity of the intermediate product HCuCH3. Finally, the results are discussed in light of low temperature matrix photoexcitation experiments and a comparison of this Cu—CH4 interaction with previous studies of the activation of the hydrogen molecule by copper is presented.

Notes: From ab initio SCF-MO calculation using a 6 - 31G** basis set, the relationship between the topology of the charge distribution and the electric field gradient (EFG) at the nuclei of the two-coordinated N atoms was determined in imines with R = H2C =, HFC =, NCHC =, and H3CHC =; di-imides with R = H, F, and CN; and the monocyclic azines with one and two N atoms in it. It was found that the N nuclear quadrupole coupling constant was determined by the nonbonded concentration of N valence shell while the asymmetry parameter has contributions from this shell and also from the rest of the molecule.

Notes: The effects of solvent-solute interactions on polarized and depolarized Raman intensity are investigated using perturbation theory, accounting for correlations in the relative orientations of the interacting transition dipoles. Two mechanisms for intensity borrowing are considered: interaction of the vibrational transition moments in the ground electronic states, and coupling of the electronic transition moments responsible for resonance Raman enhancement. The first type of interaction is shown to lead to measurable frequency shifts and depolarization ratio changes for two coupled vibrations which are infrared active and close in frequency. The second mechanism, not dependent on vibrational resonance, leads to perturbations of the depolarization ratio in resonance Raman, but not to vibrational frequency shifts.

Notes: The restricted Hartree-Fock formalism applied to quasi one-dimensional translational systems embodies slowly convergent Coulomb and exchange lattice summations. In this contribution, an algorithm based on a Filon like quadrature procedure to carry out the k-space integration of density matrix elements is analyzed and its efficiency is illustrated by its application to the linear chains of hydrogen molecules. It allows the computation of Coulomb and exchange lattice sums to their asymptotic limit, and renders obsolete the empirical procedure of guessing the number of interactions to be included in the calculations.

Notes: The hybrid method having features of ab-initio crystal orbital and ab-initio molecular cluster methods is proposed. In the approach presented the molecular crystal is treated as an infinite chain in a direction z, while two other directions are simulated by finite interactions of the molecular type. The new approach is especially useful for an investigation of anisotropic crystals. Test calculations for the carbon dioxide crystal are presented. The method was also employed for the investigation of a dissociation pathway of C—N bond in nitromethane in nitromethane crystal.

Notes: The linear combinations of Gaussian-type orbitals-fitting function (LCGTO-FF) technique has been used to calculate the binding energy and electronic band structure of a 3-atom-thick film extracted from bulk LiBeH3 in the cubic perovskite structure. The film is composed of an interior layer of LiH sandwiched between two exterior layers of BeH2, i.e., there are eight atoms per unit cell (1 Li, 2 Be, and 5 H). The calculated cubic lattice parameter for the 3-layer (a = 5.74 au) lies roughly midway between the previously published theoretical lattice parameters for a BeH2 monolayer (5.51 au) and bulk LiBeH3 in the cubic perovskite structure (5.89 au). The 3-layer film is predicted to be a semimetal (i.e., zero-gap semiconductor), unlike both bulk LiBeH3 which is predicted to be a semiconductor, and monolayer BeH2, which is predicted to be a good metal. The metallic nature of the 3-layer is due to a Be surface state that cuts across the other valence bands of the film, in good agreement with an earlier prediction that cubic perovskite LiBeH3 cleaved to expose a BeH2 layer would provide a metallic surface on an insulating substrate. The fact that the density of states goes to zero at the Fermi level is a direct result of the symmetries of the one-electron states.

Notes: A quantum mechanical time-dependent method was used to study the dynamics of dissociative adsorption and associative desorption of H2 on a flat, static surface. We used a two-dimensional model in which the molecular axis was held parallel to the surface and the diatom internuclear separation and distance above the surface were the dynamic variables. A modified London-Eyring-Polanyi-Sato (LEPS) potential described the molecule-surface interactions. The wave function for the molecule was represented by its values on a spatial grid of points. The wave function was propagated by expanding the time evolution operator in a series of Chebyshev polynomials and using the properties of the Fourier transform to calculate the kinetic energy. The computational requirements of the problem were significantly reduced by using an L-shaped grid which deletes a large number of points where it is known a priori that the wave-function amplitude vanishes. State-to-state transition probabilities were calculated as a function of the initial translational and vibrational energy for potentials with early, late, and intermediate barriers. The location of the barrier has a strong effect on the energy threshold for reaction and on the distribution of energy between vibration and translation in the products.

Notes: In this work we deal with ab initio and semiempirical calculations of single and multiple Al → Si replacements in the ZSM-5 structure. Substitutional energies for single replacements were obtained for cluster models of monomers, hexamers, and for the secondary building unit (SBU) of the zeolite by means of nonempirical SCF calculations, as well as the modified neglect of differential overlap (MNDO) method for extended clusters. The choice of the semiempirical methods for the study of multiple Si replacements by Al in the extended cluster model of the SBU is justified from the results with monomers and hexamers where the replacement energies obtained with MNDO are qualitatively the same as those from ab initio calculations. According to the results, a site occupancy order in the unit cell of the ZSM-5 network is derived from multiple Al → Si substitutions in the SBU, providing a theoretical basis for the Loewenstein-Dempsey Al sitting avoidance rules. Likewise, a Si/Al limit ratio in the Mobil FIve (MFI) zeolite, along with the corresponding Al distribution pattern in the unit cell, are also obtained.

Notes: Due to the mass effect, muonic molecular ions are about 200 times smaller than their electronic counterparts. The proximity of the nuclei in the tdμ ion results in fusion taking place within a picosecond. The properties of this ion are central to understanding the phenomenon of muon catalysis. We developed a computational method of solving the nonadiabatic Schrödinger equation for the bound and resonant states of tdμ and its isotopic analogues. The method takes into account both the Coulomb interactions and the strong nuclear forces responsible for the fusion reaction. The wave functions obtained from our method were used to predict very accurately branching ratios and transition rates relevant for various stages of the muon catalytic cycle. Knowledge of these quantities will guide the experiments and help to answer the question of feasibility of net energy production via muon catalysis.

Notes: This article describes the computation of the tunnel current in a scanning tunneling microscope (STM). The calculation accounts for the three-dimensional scattering taking place simultaneously in the first atomic layers of the sample and in the apex of the probing tip. The model is built with the following ingredients: (a) the tip is represented by a cluster of atoms attached to an otherwise planar, free-electron metal surface, and (b) the analyzed sample is a planar free-electron metal with a local potential corrugation induced by an isolated molecule or adatom. The potential barrier includes the strong bending effect due to the image-charge formation occurring as the tunneling electron crosses the gap between the tip and the sample. The specific theoretical approach designed to solve this scattering problem exploits the fast Fourier transform algorithm to construct a transfer matrix in a mixed real- and momentum-spaces representation. The total current is obtained by summing the contributions of all scattered waves traveling in the barrier between the tip and the sample, and it is studied in this article for various positions of the tip relative to the adsorbed atomic cluster. The theory is used here to simulate the scan of a model-aluminum atom on a free-electron metal substrate using electrons focused by a single-atom tungsten tip.

Notes: Bonding in transition-metal molecules presents novel features: (i) s electron bonding is overcome by multiple d electron bonding, (ii) intraatomic exchange favoring atomic magnetization competes with bonding that tends to pair the electrons, and (iii) in the heteronuclear dimers, the ionic terms may be important due to strong charge-transfer effects. The NbIr heteronuclear diatomic molecule shows all these features clearly. The cellular multiple scattering-xαβ calculation presented in this paper shows the ground state to correspond to antiferromagnetic coupling between the highly magnetic Nb atom and the Ir atom. A one-electron charge transfer from Nb to Ir was found; the result is an ionic structure, Nb+Ir-, for the dimer. The computed equilibrium distance, 4.100 a.u., corresponds to a region where d bonding strongly overcomes the s bonding, which alone would have stabilized the molecule at 5.950 a.u. At intermediate interatomic separations, 5.35 a.u., the NbIr system has a state in which all molecular orbitals are bonding with a high hybridization between the ns and (n - 1)d electrons of each atom, resulting in a (almost entirely) covalent high multiple-bond formation for this meta-stable state of the dimer.

Notes: An orthogonalization procedure is presented that allows construction of at least (n-m) vectors orthogonal to {Xj}, j equals; 1, m, by linear combinations solely among {ηi}, i equals; 1, n, n〉m, and 〈Xj/ηi〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).

Notes: The Green-function method is a well-known way to reduce the quantum mechanical problem of n electrons moving in the field of clamped nuclei to the problem of solving a one-electron Schrödinger equation (the quasi-particle equation) involving a pseudopotential (the self-energy). This method is widely used in solid-state, low-energy electron-molecule scattering, ionization, and electron attachment theory, and much work has focused on finding accurate self-energy approximations. Unfortunately, the operator nature of the fundamental quantity (Green function) in the usual quasi-particle equation formalism significantly complicates the derivation of self-energy approximations, in turn significantly complicating applications to inelastic scattering and multiconfigurational bound-state problems. For these problems or wherever the operator approach becomes inconvenient, we propose an alternative quasi-particle equation derived wholely within a configuration interaction wave-function formalism and intended to describe the same phenomenology as does the Green function quasi-particle equation. Our derivation refers specifically to electron removal but is readily generalized to electron attachment and scattering. Although the Green function and wave-function quasi-particle equations are different, we emphasize the parallels by rederiving both equations within the equations-of-motion formalism and then producing a wave-function analog of the Green function two-particle-hole Tamm-Dancoff approximation.

Notes: The transfer of a proton from A to B in AH+‥B‥C to form A‥+HB‥C is expected to enhance the binding energy of C to the remainder of the H-bonded chain since C is now adjacent to a charged ion rather than to a neutral molecule. But since the actual proton motion between A and B is typically only 1 Å or so, the interaction should be considerably less than that in isolated +HB‥C. Ab initio calculations with a variety of basis sets are used to quantitatively measure the enhancement of this binding energy. Systems investigated include the homotrimers of water and of ammonia, ammonium-formate-water, and formic acid-imidazole-water.

Notes: The effects of perturber gases, partial pressures in the range 0-50 atm, on the absorption spectra of high-n Rydbergs, n ≥ 10, in methyl iodide and benzene have been investigated. The perturbers were rare gases and H2. It has been shown that the spectroscopic energy shift Δ = Δ(ρ, n) is given by Δ = Δ°ρ, where ρ is the number density of the perturber, for n ≥ 10. The shift data can be interpreted using a Fermi model, and values of scattering lengths for perturbers can be extracted. These scattering lengths are internally consistent, independent of the absorber, and in excellent agreement with electron-swarm results. Given that the Fermi model is nonspecific and microscopic, scattering shifts and lengths for mixtures of perturber gases can be predicted. These predictions, having been verified by experiment for He/Ar mixtures, provide a means of “tailoring” any required scattering length. Finally, it is shown empirically that the determinative scattering parameter is the polarizability of the perturber, and a universal relationship a = -0.26α + 1.18 between scattering length a, in Bohr radii, and polarizability α is found to exist.

Notes: The intermolecular modes of the bifurcated water dimer are determined at the HF level using an extended basis set. In these computations, the donor libration frequency is found to be real and the bifurcated structure does not collapse toward the linear dimer. This result is contrary to all previous ab initio computations, which have predicted a Hessian with one negative eigenvalue. A good representation of other intermolecular modes, such as the libration of the acceptor, also requires an extended basis set. An interesting infrared active transition is predicted around 444 cm-1. This transition, which corresponds to the donor wag, is found in the low-temperature spectrum of water in a N2 matrix.

Notes: Perturbation theory for the rate constant of nonadiabatic solvation is presented. Miller's treatment of the RRKM theory is used for the unperturbed rate constant, and thereby the “string model” of chemical reaction is used for the description of the perturbation of solvation. The reaction path under the influence of the external force field is defined as the intrinsic reaction coordinate (IRC) that is treated as a string. The string is thrown in the external static force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of the external point charge for hydration reaction of CO2 is calculated as a preliminary model for catalytic activity of the carbonic anhydrase in the tissues and lung capillary vessels.

Notes: We have recently proven an inequality for the exact noninteracting kinetic energy density functional \documentclass{article}\pagestyle{empty}\begin{document}$ T_s [n]:\mathop {\lim }\limits_{x \to \infty } T_s [n_\lambda ^x] \le T_s [n_s^y [n] + T_S^2 [n] 〈 \infty,where{\rm }n_\lambda ^x (x,{\rm }y,{\rm }z) = \lambda n(\lambda x,{\rm }\lambda {\rm y, }\lambda z) $\end{document}. It is known that the gradient expansion through fourth order, TsGE[n], violates this inequality. Toward improving TsGE[n], we have constructed two new functionals, Ts1[n] and Ts2[n], by keeping the zeroth and second orders in TsGE[n] and replacing the fourth order with two simple terms, respectively, so that these new functionals satisfy the inequality. Numerical tests are presented for Ts1[n], Ts2[n], and TsGE[n] and for the gradient expansion through second order. Hartree-Fock and hydrogenic atomic densities are employed.

Notes: Two possible reaction paths for the pyrolysis of the ethylester of glyoxylic acid have been studied by ab initio molecular orbital calculations. The basis sets 3-21G and 6-31G* have been used, and electron correlation has been included by Møller-Plesset calculations up to fourth order. Our calculations indicate that the reaction leading to acid and ethylene through a 6-membered ring transition state is favored relative to a process involving a formyl hydrogen transfer via a 5-membered ring to the alkyl unit leading to ethane, CO, and CO2. The predicted activation energies for these two reactions obtained at the highest level of calculation, MP4(SDTQ)/6-31G*, are 50.4 and 71.7 kcal/mol, respectively. The transition states have RHF wave functions that are stable relative to UHF solutions using the 3-21G basis. The geometry of the transition states and IRC following indicate that both reactions are strongly asynchronous: The C—O bond rupture is virtually completed before hydrogen transfer occurs. For comparative purposes, analogous calculations have been performed for the ethylester of formic acid, where it is confirmed that a 6-membered ring transition state is preferred relative to a 4-membered one by around 42 kcal/mol at the highest level of calculation.

Notes: A time-dependent molecular orbital method has been developed to study charge transfer in collisions of ions with metal surfaces at energies between 1 and 100 au. A set of localized basis functions consisting of generalized Wannier functions for the surface and s- and p-atomic functions for the ion, is used to separate the system into primary and secondary regions. An effective Hamiltonian and time-dependent equations for the electron density matrix are obtained in the primary region, where most charge transfer occurs. The equations for the electron density matrix are solved with a linearization scheme. The method is suitable to study atomic orbital orientation for collisions of ions and surfaces. A model calculation for Na+ + W(110) collisions with a prescribed trajectory is presented. The interaction potentials between the W(110) surface and Na+ 3s and 3p orbitals are calculated from Na+ pseudopotentials. Results show that the yield of neutralized atoms in 3p states changes as the collision energy is lowered.

Notes: It is shown that the dispute about the conditions for physical admissibility of Schrödinger wave functions may be settled if the following two questions are clarified: (a) Are these condittions rooted in the foundations of quantum mechanics or invoked only for particular physical models? (b) Do we consider either the position-space wave function or the momentum-space wave function? Both the case of closed states and scattering states are considered. Some general remarks about these conditions are made in the Conclusion.

Notes: The cupula of the supraorbital neuromast in the lateral line canal of the clown knifefish contains vertical columns. In the central region of the cupula overlying the macula, these columns are densely packed, are relatively constant in size, and run from the base of the cupula to the surface of the cupula which is exposed to canal fluid. There are two types of columns, dark and light, which form elliptical compartments in planes of section that cut across the columns; the cupula therefore has the appearance of mosaic tile in such sections. The dark compartments contain tubules that extend from the base of the cupula at the junction with the macula to the top of the cupula. Each tubule is associated with the kinocilium of a single hair cell. The lateral parts of the cupula, not overlying the macula, also contain compartments, but these compartments differ in size and structure from those in the central region. In addition to the compartments, the central region of the cupula also contains spherical aggregates of droplets. These small aggregates, termed mora, are found principally in a layer within the central region of the cupula, but are also found outside this layer. Because of their light-reflecting properties, the mora can be used for noninvasive optical measurements in vivo of the motion of the cupula.

Notes: Light and electron microscopic examination demonstrated two types of non-endocrine agranular cells, cavity boundary cells and stellate cells, in the adenohypophysis of the South American lungfish, Lepidosiren paradoxa. The cavity boundary cells line the hypophyseal cleft and diverticulum and display few microvilli, occasional cilia, prominent junctional complexes, and many cytoplasmic microfilaments. The stellate cells are scattered in the glandular parenchyma and are devoid of microvilli and cilia. When adjacent, they are connected to one another by desmosomes. Pinocytotic vesicles or caveolae are frequently seen along the plasma membrane of the agranular cells adjoining the endocrine cells or abutting on the basement membrane. Possible roles of the agranular cells, physically and metabolically supportive functions, are discussed on the basis of their ultrastractural features.

Notes: The paired organ of Bellonci protrudes from the optic lobe of the giant Antarctic isopod, Glyptonotus antarcticus. It is linked to the cortex by a broad peduncle. No connection to the cuticle or “sensory pore organ” was found. A cluster of sensory-like cells forms two outer ciliary segments branching into numerous microvilli with microtubules. The putative sensory somata are irregular in shape and contain a very high density of glycogen granules. The two outer segments sprout from two pits of the soma in different directions, forming a right angle. Glial cells wrap around the sensory cells and also delimit lacunae into which bundles of microvilli project. These lacunae contain electron-dense granules of small size and with species-specific patterns. Lacunae and dense granules show features typical of a degeneration process in the sensory cells.This general morphology corresponds to the unilobular type of organ of Bellonci, known in other isopods; it differs from the plurilobular type with onion bodies found in other Crustacea.

Notes: Neuromast structure in Rana cancrivora larvae was observed by scanning and transmission electron microscopy. Neuromast units, each being composed of two or three neuromasts, are arranged in several well-defined lines in the head, body, and tail regions. The structure of neuromasts in these three regions is basically identical. The neuromast is composed of sensory, sustentacular, and mantle cells. The top of each neuromast has a hillocklike appearance, and is surrounded by four to six epidermal cells with tight intercellular junctions. Long kinocilia and many stereocilia occur in the apex of the neuromasts and are surrounded by numerous microvilli. Numerous granules are present on the apical portions of the mantle and the sustentacular cells. Four or five trapeziform mantle cells are connected closely with each other to form the shell of the neuromast. Large intercellular spaces occur between the mantle cells and the cells of the inner epidermal layers, and between the cells of the inner epidermal layer. Thus, at the apical parts of the neuromast intercellular junctions are tight and the intercellular spaces are more dilated in more basal areas. Morphologically the neuromasts of R. cancrivora larvae resemble those of generalized pond anurans, based on the grouping of Lannoo (Journal of Morphology 191:115-129, 1987a), although larvae of this species inhabit brackish water.

Notes: Orbital gland structure of the Atlantic bottlenose dolphin, Tursiops truncatus, was examined at the macroscopic, light microscopic, and electron microscopic levels. The gland completely encircles the ocular globe in a belt-like fashion near the conjunctival fornix but is considerably more developed medially. Duct openings are scattered throughout the fornix and over the surface of the palpebral conjunctiva. Microscopically, the gland has a tubuloalveolar arrangement; alveolar cells contain numerous secretory vesicles which can be interpreted as two structural types by light and electron microscopy. Histochemical staining demonstrates that both types contain glycosaminoglycans. Lipid analysis of the glandular secretion (dolphin tears) shows them to be non-oily and to contain only negligible amounts of cholesterol, triglycerides, phospholipids, and free fatty acids. The secretion is clear, slippery, and viscoelastic and well-adapted to protecting the eye and to reducing frictional forces between the eye surface and surrounding seawater.

Notes: The muscle fibers of the feline biceps femoris have tapered ends, across which tension is transmitted to the endomysium. The angle of taper of 11 ends, measured on scanning electron micrographs, varied between 0.16° and 1.18°. The muscle fibers are highly variable in cross-sectional shape. The shape of the fibers has been quantified as the ratio (form factor [FF]) of the measured perimeter to the calculated circumference of a circle having an area equal to that contained by the fiber perimeter. The FF for 173 terminal portions of fibers varied between 1.06 and 1.85 and was found to have a highly significant negative correlation with sarcomere length. The slope of the regression line suggests that the fibers maintain both volume and surface area as they change length. These studies suggest that isovolumic muscle fibers maintain a constant surface area by changing shape as they change length.

Notes: Salt glands of the domestic duck Anas platyrhynchos differ from those of the herring gull Larus argentatus and other birds. In ducks, each salt gland consists of distinct medial and lateral segments. Centrally located drainage ducts that extend along the entire length of these medial and lateral segments collect hypertonic fluid secreted by an array of lobules. Each lobule is formed by a single mass of branched tubules in which the direction of capillary blood flow is opposite to that of the secreted fluid. This fluid drains from the medial segment through an external duct that opens into the nasal cavity at the base of the vestibular fold. A duct from the lateral segment loops and opens onto the surface of the nasal septum. The structure and function of the secretory cells is reviewed briefly within the context of our study of the configuration of duck nasal salt glands.

Notes: A contrast radiographic study of pelvic fin drainage in rays reveals considerable differences in patterns of drainage among the species studied. The “typical” shark pattern of drainage, to the lateral abdominal vein, is also found in rays with shark-like morphology. However, variation in the connections of pelvic fin veins to muscular and cutaneous vessels of the pectoral fin occurs in the more “derived” batoid groups, with marked differences between rays of similar external morphology and mode of locomotion. There is a positive association between the pattern of fin drainage and the number of radial cartilages in the posterior (metapterygial) lobe of the pectoral fin. Variation in shark pelvic fin drainage may also be related to differences in pectoral fin morphology.

Notes: Dissections of Sudan black B stained specimens reveal that, of a complex of medial, intermediate, and lateral muscles of skates, presumed homologous to the cucullaris of sharks, only the lateral muscle is innervated by a branch or branches of the vagus and is inserted, in part, to the fused pharyngobranchials of the caudal visceral arches. The medial and intermediate muscles are supplied by separate branches of rostral spinal nerves and do not attach to the branchial skeleton. The lateral muscle therefore is the most likely homologue of the cucullaris (trapezius) of sharks and perhaps other fishes and tetrapods. The medial and intermediate muscles appear to be part of the axial musculature.

Notes: An immunocytological study of four different parts of the gut of Helix aspersa clearly demonstrates the presence of many cells and fibers immunoreactive toward antibodies directed to vertebrate (α, β-endorphin, α, β-MSH, ACTH 1-24 and ACTH 17-39, met-enkephalin, somatostatin, insulin, glucagon, P.P., serotonin) or invertebrate (FMRF-amide) peptides.These results are evidence of the presence of different substances related to known peptides or amines in the epithelial and connective tissue cells and nerve fibers of the snail gut. Immunocytochemistry may help to elucidate the morpho-functional characteristics of the enteroendocrine cells of H. aspersa.

Notes: A histochemical investigation of kidney and lower intestine of the European starling (Sturnus vulgaris) shows no carbonic anhydrase activity in proximal convoluted tubules, although activity is seen in similarly prepared sections of rat proximal tubules. Early distal tubule cells in the starling are stained throughout the cytoplasm and at the apical and highly infolded basolateral membranes. Late distal tubules lose apical activity and have reduced basolateral infolding, resulting in less intense staining. Darkly stained intercalated cells appear in the connecting tubules and cortical collecting ducts. Both of these segments also show intense basolateral staining. Medullary cones of the starling are highly organized, with central zones containing unstained thin descending limbs of loops of Henle, surrounded by both medullary collecting ducts with only scattered cells staining for enzyme, and by thick ascending limb segments. The latter contain many uniformly stained cells intermingled with occasional unstained cells. Scattered cells of the starling colonic villi demonstrate intense apical brush border membrane staining as well as cytoplasmic staining. Cells lining the cloaca stain less intensely. A biochemical assay for carbonic anhydrase was used to quantify enzyme activity in these tissues. Starling kidney contained 1.96 ± 0.33 (mean ± SEM) enzyme units/mg protein, less than half the activity seen in rat kidney. Stripped colonic epithelium contained 0.66 ± 0.15 enzyme units/mg protein. These quantitative results correlate well with the interpretations derived from the histochemical observations. The lack of proximal tubule carbonic anhydrase activity suggests that the avian kidney relies more on distal nephron segments to achieve net acidification of the urine.

Notes: The orientation of the fibers in the dermis of the tiger salamander, Ambystoma tigrinum, undergoes a dramatic repatterning at metamorphosis. The pre-metamorphic, larval dermis is a tight layer composed of crossed fibers that wind helically around the trunk. This condition is retained by neotenic adults which do not undergo metamorphosis. In contrast, the metamorphosed adult dermis consists of a superficial, loose network of fibers invested with large multicellular glands - -the stratum spongiosum - and a deeper tight layer of fibers - the stratum densum. However, unlike the crossed fibers of the pre-metamorphic dermis, there is no preferred orientation to the fibers in either layer of the post-metamorphic dermis.In order to evaluate whether these two distinctly different fiber patterns are constructed from biochemically similar fibers, the collagen types present in the pre- and post-metamorphic dermis were determined using SDS-polyacrylamide gel electrophoresis. Type I collagen is the predominant collagen of the dermis and the same major collagen types are present for all individuals, whether preor post-metamorphic. Thus, the major types of collagen that compose the dermal fibers do not change during metamorphic repatterning of the dermis.

Notes: In the first half of this century, several workers observed small, seemingly glandular structures attached to the ampullate glands of spiders. Hence, they were termed accessory ampullate glands. In juvenile Araneus cavaticus, two pairs of these structures are present (starting at least with third instars), one pair attached to the major ampullate (MaA) glands and the other pair attached to the minor ampullate (MiA) glands. In adults, two pairs of accessory MaA glands and two pairs of accessory MiA glands are present. The two latter-formed pairs of accessory ampullate glands are clearly the remnants of those ampullate glands which atrophy shortly after adulthood is reached. Morphological similarities between these accessory ampullate glands and those present in juveniles provide an indication that the latter also have their origin in functional ampullate glands.A reduction in the number of ampullate glands following the last molt occurs in many spiders. The reason(s) for these reductions is unknown. In penultimate spiders close to ecdysis, we have observed that while the larger pairs of MaA and MiA glands (those that are retained in the adult) are undergoing molt-related changes which apparently render them nonfunctional, their smaller counterparts are seemingly unaffected and functional. This raises the possibility that the principal role of the smaller ampullate glands may be to assume functions during the pre-ecdysial period which are normally in the domain of the larger ampullate glands. If true, then their degeneration after the last molt would make economic sense.The presence of cylindrical spigots in juvenile females starting with fourth instars is documented.

Notes: Three basic types of cells are distinguished in the rat vomeronasal epithelium at birth: bipolar neurons, supporting cells, and basal cells. Neurons at this time include both immature and differentiated cells. By the end of the first postnatal week, all neurons show morphological signs of maturity in their cytoplasm, including abundant granular and smooth endoplasmic reticulum, neurotubules, dense lamellar bodies, apical centrioles, and tufts of microvilli. During the third week microvilli are more frequently encountered and appear to be longer and more branched. Supporting cells appear well-developed by the second day after birth. During the first ten days of life, supporting cells lose their centrioles and all of the complex associated with ciliary generation in the apical zone. Basal cells appear to be more numerous in newborns than in older animals. Protrusions projecting into the lumen are frequently observed in the epithelium of newborn animals, both on the dendrites of neurons and on supporting cells. After the third week, such protrusions are only observed in the transitional zone between the sensory and the non-sensory epithelia of the vomeronasal tubes. In this transitional zone, a fourth cell type showing apical protrusions with microvilli differentiates. Cytoplasm in this type resembles that of neighboring ciliated cells but has no cilia or centrioles. These transitional cells are considered to be cells in an intermediate state of differentiation, between that of the differentiated neurons and supporting cells of the sensory epithelium and that of the predominate ciliated cells of the non-sensory epithelium. The results suggest that by the end of the third week the vomeronasal epithelium is morphologically mature.

Notes: The wall of the stomach of the tigerfish is described and compared with that of other vertebrates. Light microscopic and ultrastructural characteristics of the stomach wall correspond to a large extent to those of other vertebrates, although some differences are found. The mucosa contains (1) surface epithelium characterized by narrow columnar cells with abundant mucous granules; (2) gastric glands consisting of pepsinogenic cells of variable height, containing tubulovesicles and bearing microvilli; (3) five granulated cell types located basally in the epithelium (types 1-5); and (4) lamina propria and muscularis mucosae. Connective tissue separating smooth muscle fibers of the muscularis mucosae constitutes a stratum compactum. The submucosa contains a loose connective tissue, a tunica muscularis of inner circular and outer longitudinal layers, and a serosa of mesothelium and subjacent connective tissue. Immunocytochemical tests with antisera to five polypeptides show gastrin/cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP) immunoreactivities in some cells of the gastric glands, and somatostatin in cells lying among epithelial cells lining the gastric luminal surface or gastric pits.

Notes: Previous studies by Stephens and McNulty and Strecker and Stephens have demonstrated that foil barriers placed between the mesonephros and lateral plate at stages 12 to 15 inhibited limb development, but foil barriers placed between the neural tube and somites at stages 11 to 12 resulted in limbs with normal skeletal patterns. It was concluded that some influence present in the paraxial region of the embryo at stages 11 to 15 is necessary for normal limb development. The present study was undertaken to localize that influence more precisely. Foil barriers were placed in the lateral edge of the somites or segmental plate of stage 10 to 15 chick embryos. Barriers placed into stage 13 to 15 embryos resulted in chicks with normal limbs, but barriers placed into stage 10 to 11 embryos resulted in chicks with defective limbs. Barriers inserted just lateral to Hensen's node at stages 6 to 8 resulted in embryos with defective or absent wings. We also grafted stage 4 to 9 presumptive limb territories with and without Hensen's node. Explants without Hensen's node formed limb-like structures in 1% of the cases. Explants with Hensen's node formed limb-like structures in 27% of the cases. When barriers were implanted and a node was placed on the lateral side of the barrier, limbs formed in 40% of the cases. These data suggest a medial to lateral progression of some as yet unknown morphogenetic influence necessary for normal limb development and we hypothesized that the influence may initially emanate from Hensen's node.

Notes: The limb bone skeleton of the moa, a family of extinct ratite birds endemic to New Zealand, is described with particular reference to the anatomical and functional significance of osteological landmark form variation. The results generally support the existing classification of moa. Four genera, Megalapteryx, Anomalopteryx, Dinornis, and Pachyornis, were found to be evolved within moa, with Emeus and Euryapteryx possibly being more primitive. Megalapteryx was found to be less mobile than other moa genera. The Dinornis species were found to be more cursorial and more mobile relative to other moa. They may also have had a different center of gravity. A marked development of the lower leg in Anomalopteryx suggested a digging habit associated with food procurement.

Notes: A detailed description of muscular and skeletal features of the pelvi-cloacal region of the amphisbaenian Blanus cinereus reveals that the species has real hind limbs articulating with a real pelvic girdle. Arguments support this homology: 1) a link with the vertebral column; 2) a movable articulation, showing all the features of a diarthrosis, between the femur and the acetabulum; 3) all the long bone characteristics for the femur which distally bears a horny element. The morphological peculiarities of the amphisbaenian pelvic girdle are generally close to those of lizards, but the pubis seems to be more reduced. For the same number of precloacal vertebrae, the amphisbaenians have more appendicular elements than lizards have, and this composition recalls that of the Leptotyphlopidae, Aniliidae, and Boidae. The account provides more information concerning the aponeuro-tendinous system associated to the skeleton of the girdle and the hindlimb, the musculature, and the interrelations between the different structures of the pelvi-cloacal region.

Notes: Programmed cell death is an integral and ubiquitous phenomenon of development that is responsible for the reduction of wing size in female moths of Orgyia leucostigma (Lymantriidae). Throughout larval and pupal life, cells of the wing epithelium proliferate and interact to form normal imaginal discs and pupal wings in both sexes. But at the onset of adult development, most cells in female O. leucostigma wings degenerate over a brief, 2-day period. Lysosomes and autophagic vacuoles appear in cells of the wing epithelium shortly after it retracts from the pupal cuticle. Hemocytes actively participate in removing the resulting cellular debris. By contrast, epithelial cells in wings of developing adult males of O. leucostigma do not undergo massive cell death. Wing epithelium of female pupae transferred to male pupal hosts behaves autonomously in this foreign environment. By pupation, cells of the female wing apparently are committed to self-destruct even in a male pupal environment. Normal interactions among epithelial cells within the plane of a wing monolayer as well as between the upper and lower monolayers of the wing are disrupted in female O. leucostigma by massive cell degeneration. Despite this disruption, the remaining cells of the wing contribute to the formation of a diminutive, but reasonably proportioned, adult wing with scales and veins.

Notes: We describe the localization of lipids in the wall and superficial ooplasm of the largest avian ovarian follicles by the use of different fixatives and light and electron microscopy. We demonstrate that each yolk globule is always accompanied by one or more highly osmiophilic and sudanophilic alcohol insoluble yolk masses, which we have called satellite yolk. Together with the protein containing yolk globule it forms an integral morphological part of a compartmentalized, bipartite yolk system. Cytochemical, histoautoradiographic, biochemical, and light and electron microscopical aspects of satellite yolk were studied. At the start of satellite yolk formation in the 3-4 mm diameter follicle (when the oocyte begins to yellow) the distribution of the microcirculation of the follicle wall becomes printed on the underlying superficial ooplasm of the oocyte. The oocyte then presents so-called yolk mountains (containing satellite yolk), only localized below the thecal capillary sinus and not below the efferent and radially perforating thecal veins (black hole regions). We also describe the structural continuity between the thecal intercellular spaces and the microvilli-associated extracellular spaces of the granulosa cells via the basement membrane. The thecal cells present centripetal extensions into the basement membrane and the basement membrane material extends centripetally into the granulosa microvillar channels. Therefore, at least two cellular barriers are crossed when fat or fat precursors are transported from the thecal capillary sinus to the ooplasm.

Notes: Embryos of the poeciliid Heterandria formosa develop to term in the ovarian follicle in which they establish a placental association with the follicle wall (follicular placenta) and undergo a 3,900% increase in embryonic dry weight. This study does not confirm the belief that the embryonic component of the follicular placenta is formed only by the surfaces of the pericardial and yolk sacs; early in development the entire embryonic surface functions in absorption. The pericardial sac expands to form a hood-like structure that covers the head of the embryo and together with the yolk sac is extensively vascularized by a portal plexus derived from the vitelline circulation. The hood-like pericardial sac is considered to be a pericardial amnion-serosa. Scanning and transmission electron microscopy reveal that during the early and middle phases of development (Tavolga's stages 10-18 for Xiphophorus maculatus) the entire embryo is covered by a bilaminar epithelium whose apical surface is characterized by numerous, elongate microvilli and coated pits and vesicles. Electron-lucent vesicles in the apical cytoplasm appear to be endosomes while a heterogeneous group of dense-staining vesicles display many features characteristic of lysosomes. As in the larvae of other teleosts, cells resembling chloride cells are also present in the surface epithelium. Endothelial cells of the portal plexus lie directly beneath the surface epithelium of the pericardial and yolk sacs and possess numerous transcytotic vesicles. The microvillous surface epithelium becomes restricted to the pericardial and yolk sacs late in development when elsewhere on the embryo the non-absorptive epidermis differentiates. We postulate that before the definitive epidermis differentiates, the entire embryonic surface constitutes the embryonic component of the follicular placenta. The absorptive surface epithelium appears to be the principle embryonic adaptation for maternal-embryonic nutrient uptake in H. formosa, suggesting that a change in the normal differentiation of the surface epithelium was of primary importance to the acquisition of matrotrophy in this species. In other species of viviparous poeciliid fishes in which there is little or no transfer of maternal nutrients, the embryonic surface epithelium is of the non-absorptive type.

Notes: The flagellum of the thysanopteran spermatozoon has been examined by electron microscopy and computer-aided image analysis. The flagellum consists of 27 microtubular elements that probably are formed as outgrowths from three separate basal bodies. Nine of the elements are normal microtubular doublets that carry dynein arms and nine are doublets without dynein arms. The remaining nine elements are microtubular singlets that apparently bear dynein arms and have the same appearance as A-subtubules of microtubular doublets. The 27 elements are arranged in a fixed pattern that consists of nine groups, each of which begins with a microtubular singlet and ends with an arm-less microtubular doublet. Computer-aided image analysis has shown that the A-subtubules of the doublets and the microtubular singlets have lumens with very similar patterns. The sperm tail is known to have some motility; it generates fast waves running along its length. The amalgamated axonemes hence act as a functional flagellum. The thysanopteran sperm tail is the only type of flagellum known to us that consists of microtubules in a highly asymmetric array.

Notes: Many arachnids lack extensor muscles at the femoropatellar (knee) joint of their legs and extend this joint with hydraulic pressure during locomotion. Pressure is generated through compression of the prosoma, but there is disagreement about which muscles are involved in this process. Many arachhnologists consider contraction of the musculi laterales, a group of modified extrinsic leg muscles, as the cause of high prosomal pressure and regard hydraulic extension as a derived feature. However, integration of results from phylogenetic and comparative anatomical studies supports the view that hydraulic extension is primitive in Arachnida and that fluid pressure is generated by contraction of endosternal suspensor muscles.The functional predictions of the musculi laterales and endosternite hypotheses were tested by measuring muscle activity and prosomal pressure during unrestrained locomotion in a primitively “extensorless” arachnid, the giant whipscorpion. The results corroborate the endosternite model and refute the musculi laterales model. Changes in the prosomal pressure baseline were correlated with changes in endosternal muscle activity, while the musculi laterales fired in a step-coupled pattern of discrete bursts that appeared to be incapable of generating the pressure observed during locomotion. Step-coupled fluctuations in prosomal pressure were observed but were apparently caused by rapid flexing of the femoropatellar joints of the fourth leg pair rather than contraction of the musculi laterales.

Notes: In the fungiform papilla of Rana esculenta (Anura Ranidae), the Ca++-ATPase is mainly distributed on the basolateral membrane of the sensory area cells (i.e., neuroepithelial, supporting, and mucous cells). Apical membranes of all cells facing the surface present a slight enzymatic activity. Lateral wall cells have a strong Ca++-ATPase activity on basolateral and apical membranes. Strong Na+, K+-ATPase activity occurs on the apical surface of neuroepithelial cells. Ca++-ATPase activity is absent on the surface of endothelial cells of the capillaries located under the sensory area. These observations lead us to conclude that the sensory area of fungiform papilla is the selective way for calcium influx. Furthermore the absence of ATPase activity on the surface of the endothelial cells indicates that there is no functional barrier to calcium influx into capillary, and that calcium can be removed by vessels from the sensory area.

Notes: Spermatogenesis and sperm ultrastructure were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in the longidorid Xiphinema theresiae. All germ cell stages, except spermatogonia, are present in the testes of young adult males. The nonflagellated, slightly elongated sperm displays little intraspecific variation and, although never polarized into a head and tail region, has a remarkably precise form, with a high degree of internal organization. Incipient fingerlike pseudopodia appear in the young spermatid and increase to such an extent that the adult sperm has a conspicuous “woolly” appearance. Microfilament bundles encircle the perinuclear mitochondria in the spermatid, and seem to be closely associated with the evaginated plasma membrane, especially in the spermatozoon. A large nucleus with nuclear envelope is prominent in the spermatocyte, but the envelope is absent in the young spermatid. Mitochondria are present in all germ cell stages and undergo certain morphological changes (e.g., in size and number, presence or absence of cristae), as well as changes in intracellular movements during spermatogenesis. Membranous organelles are prominent in the spermatocyte, but disappear in the older spermatid. Annulate lamellae and a residual body (i.e., cytophore) are conspicuous in the spermatocyte and spermatid, respectively; the spermatozoon clearly lacks a refringent body (i.e., acrosome).

Notes: The morphology and distribution of muscle spindles of jaw and tongue muscles in the mallard were examined in serial transverse sections of single muscles and in horizontal sections of a whole head. Our observations on spindle morphology are in agreement with previous descriptions of spindles in birds. Some spindles differ in their innervation and the pattern of intrafusal muscle fibers. The spindles of individual adductor and pterygoid muscles are distributed unevenly. Some adductor muscles lack spindles, whereas those of other muscles are confined to limited areas. Jaw opening muscles and extrinsic tongue muscles lack spindles. The stretch of extrafusal muscle fibers could be estimated from the difference in sarcomere length for birds with the beak open and closed. Not all muscle fiber groups are stretched evenly over the whole range of jaw opening. Only those fiber groups that are continuously stretched during jaw opening contain spindles.

Notes: Living embryos of three species of South American annual fishes, Cynolebias constanciae, C. nigripinnis, and C. whitei, were observed from fertilization through the 10-somite stage. A description of normal stages of development applicable to all three species of Cynolebias is presented. Cleavage (stages 1-10) is meroblastic and produces a typical teleost blastoderm. Following cleavage (stages 11-13) blastomeres segregate into two populations, viz., (1) a population of deep blastomeres that will disperse as single motile cells, and (2) a hemispherical shell of outer blastomeres that flattens to form an enveloping cell layer (EVL). When epiboly of the EVL and the yolk syncytial layer (YSL) commences (stage 14), deep blastomeres clump together as a consolidation mass and then migrate outward as single cells on the YSL. When epiboly is concluded (stage 19), deep blastomeres have completely dispersed. If diapause does not intervene, the dispersed phase lasts only a few days. Subsequently, the dispersed cells come together to form a definitive aggregate (stage 27). Embryogenesis within the reaggregated mass of previously dispersed cells produces a typical teleost embryo.Early development in Cynolebias resembles that of other South American annual fishes, such as Austrofundulus, in that a phase of deep blastomere dispersion and reaggregation spatially and temporally separates epiboly from embryogenesis. Several features of development markedly differ from Austrofundulus. There are far fewer (250 vs. 2,500) deep blastomeres. Deep cells of Cynolebias are flattened rhomboids with filipodial extensions in contrast to the amoeboid cells of Austrofundulus. Blastomeres of dispersion and reaggregation stages in Cynolebias send out numerous cell surface extensions onto the YSL and in contact with one another, and often line up in rows as do some African annual fishes, e.g., Nothobranchius. During Dispersion II (stage 21), Reaggregation I (stage 22), and Reaggregation II (stage 23), deep cells move in an oriented pattern with respective mean velocities of 3.48 ± 0.91, 1.28 ± 0.46, and 1.31 ± 0.31 μm/minute. Cells move toward a granular mass of unknown composition, located at the YSL-yolk interface in the lower hemisphere of the egg. This mass appears to coincide with the site of cell reaggregation.

Notes: Several surfperches (Embiotocidae), including the black surfperch, Embiotoca jacksoni, exhibit a specialized prey handling behavior known as winnowing, in which ingested food and non-nutritive debris are separated within the oropharyngeal cavity. Prey items are swallowed, and unpalatable material is ejected from the mouth. Winnowing is believed to play an important role in the partitioning of food resources among sympatric embiotocids. We present a mechanistic model for this separative prey processing based on high-speed video analysis, cineradiography, electromyography, and buccal and opercular cavity pressure transducer recording.Winnowing by embiotocids is characterized by premaxillary protrusions repeated cyclically with reduced oral gape. Protrusion is accompanied by depression of the hyoid apparatus and adduction of the opercula. Alternating expansion and contraction of the buccal and opercular cavities generate regular pressure waveforms that indicate bidirectional water flow during processing. Separation of food from debris by Embiotoca jacksoni occurs in three phases. The prey-debris bolus is transported anteriorly and posteriorly within the oropharyngeal cavity and is then sheared by the pharyngeal jaws. Mechanical processing is complemented by the rinsing action of water currents during hydraulic prey transport.The feeding apparatus of Embiotoca jacksoni is functionally versatile, although not obviously specialized relative to that of nonwinnowing surfperches. Protrusion of the premaxillae and depression of the hyoid apparatus are critical to both prey capture and subsequent prey processing. The pharyngeal jaws exhibit kinematic patterns during separation of food from debris distinct from those observed during mastication of uncontaminated prey. This behavioral flexibility facilitates resource partitioning and the coexistence of E. jacksoni in sympatric embiotocid assemblages.

Notes: Quantifying shape is a broad problem in the morphological sciences. Most techniques for numerically describing shape abstract the shape into the most logical ideal Euclidean dimension. The fractional, or fractal, dimension is a simple computation that expresses shape in real, rather than ideal, space. The structured walk technique developed for the fractal analysis of rugged boundaries is applied here to the contour of the human sagittal suture in order to discriminate the separate morphological patterns of interfingering and interlocking. These attributes contribute differentially to the suture's “complexity,” a concept often used in biomechanical hypotheses. Previous techniques for estimating sutural complexity do not isolate small-scale from large-scale morphological patterns. Results indicate that despite the visual appearance of great variation, human sagittal sutures are remarkably consistent in the degree of complexity expressed separately by large-scale interfingering lateral excursions and small-scale interlocking ruggedness. There is no significant correlation between the absolute or bregma-lambda chord length of the human sagittal suture and its degree of complexity as determined by the structured walk technique.

Notes: Spermatophores in a squid, Todarodes pacificus, were observed by light and electron microscopy and were further analyzed by X-ray microanalysis (XMA) of frozen thin sections. Each spermatophore consists of a sperm mass, a cement body, an ejaculatory apparatus, and some fluid materials, all of which are covered by an outer tunic. The outer tunic consists of about 20 membranous layers, each containing straight, parallel microgrooves. Each layer's microgroove pattern is roughly in an orthogonal arrangement with respect to the next layer's pattern. The sperm mass, which is the only cellular component, consists of a sperm rope which is coiled more than 500 times. Most of the spermatozoa in the rope are arranged regularly and are enveloped in materials which are well-stained by Alcian blue. The cement body is located between the sperm mass and ejaculatory apparatus and has a hard outer shell with an arrowhead-like structure, presumably for penetration into the tissue of the female. Calcium and phosphorus are present in the shell of the cement body, which also has an affinity for alizarin red. The ejaculatory apparatus consists of two tubes, designated as the inner tunic and the inner membrane.After the spermatophoric reaction, a sperm reservoir is formed at the anterior end of the extruded and inverted ejaculatory apparatus. The sperm reservoir, which encases the sperm mass, is composed of the cement body at the anterior end and the inner tunic of the ejaculatory apparatus at the posterior end.

Notes: Spermiogenesis in the South American leptodactylid frog Odontophrynus cultripes was analyzed ultrastructurally. The spermatids undergo morphological modification while still enclosed in microtubule-rich processes of Sertoli cells. Electron-dense plates resembling junctional structures appear in regions at which the spermatids lie in close contact with the surface of Sertoli cell processes. Spermatid differentiation can be divided into five distinct stages based mainly on chromatin condensation. In the late stages, the densely compacted chromatin loses reactivity to ethanolic phosphotungstic acid (E-PTA). Helical arrangements of microtubules appear in the cytoplasm that surrounds the spermatid nucleus after the second stage. The acrosomal vesicle differentiates into a cone-shaped acrosome that caps the anterior region of the nucleus. The connecting piece, located in the flagellum implantation zone, has transverse striations, and is continuous with the axial rod. The tail is formed by a 9 + 2 axoneme, an undulating membrane, and an axial rod that is rich in basic proteins as demonstrated by E-PTA staining.

Notes: Morphology of the chromaffin cells of Triturus cristatus during a complete annual cycle has been investigated. General ultrastructural characteristics are similar for all chromaffin cells, including numerous small mitochondria, well-developed Golgi apparatus and rough endoplasmic reticulum with short cisternae. The primary difference among cells is the type of the chromaffin granules they posses. These are of two kinds: adrenalin (A) and noradrenalin granules (NA). Both types are simultaneously present in the chromaffin cells but with different ratios during the year. During December-January and May-August, NA granules largely prevail, while in September-November and February-April, A and NA granules are present in about equal quantities. The total quantity of catecholamine granules, however, is relatively constant throughout the year. These findings suggest that T. cristatus has a single type of chromaffin cell, the granule content of which varies according to different functional states. The catecholamines are apparently discharged by exocytosis.

Notes: The palatoquadrate and associated dermal bones have significant evolutionary transformations among teleostomes and provide numerous features that characterize teleostomian subgroups. The palatoquadrate forms the upper part of the mandibular arch and is present as a single cartilaginous element in the early ontogeny of teleostomes, except for some advanced teleosts such as siluroids where it is divided into pars autopalatina and pars pterygoquadrata. During ontogeny, the palatoquadrate may ossify as a unit, with a pars autopalatina (absent in Acanthodii), pars quadrata, and pars metapterygoidea in teleostomes (e.g., primitive acanthodians and actinopterygians, onychodonts, and rhipidistians). However, the palatoquadrate may remain cartilaginous (e.g., chondrosteans) or it may ossify as separate elements (e.g., autopalatine, metapterygoid, and quadrate) as occurs in advanced acanthodians, Polypterus and advanced actinopterygians, and advanced actinistians. From the single-unit pattern, separate autopalatine, metapterygoid, and quadrate evolve in parallel in the three teleostomian subgroups. Therefore, it is necessary to distinguish between actinopterygian and actinistian autopalatines and among acanthodian, actinopterygian, and actinistian metapterygoids and quadrates. A palatoquadrate fused with the neurocranium occurs in parallel in dipnoans.There are differences in the timing of ossification of the autopalatine, metapterygoid, and quadrate. The autopalatine ossifies late in ontogeny in Polypterus, Amia, and primitive teleosts (absent in lepisosteids and osteoglossmorphs), whereas both metapterygoid and quadrate ossify early in ontogeny. The early ossification of the autopalatine is characteristic of clupeocephalan teleosts. During ontogeny, tooth plates (not forming a separate dermometapterygoid) fuse with the metapterygoid in actinopterygians.Pars autopalatina, pars metapterygoidea, and pars quadrata are regions at the three corners of the single-unit palatoquadrate present in primitive teleostomes; there are no clear limits among these regions, but they may be identified by their processes, articular facets, and topographical relationships with surrounding bones and the orbit. Autopalatine, metapterygoid, and quadrate are chondral bones, perichondrally ossified. Dermal elements such as dermopalatine(s), entopterygoid, ectopterygoid, and tooth plates may cover the palatoquadrate medially. The predermopalatine that originates in front of pars autopalatina in Cladistia and the “dermopalatine” that lies medial to the ectopterygoid in Ginglymodi are specializations of these groups. A dermopalatine fused with the autopalatine is characteristic of clupeocephalan teleosts. Highly specialized tendon bone pterygoids are found in some teleosts (e.g., siluroids). The presence of both maxilla and lacrimal lateral to the pars autopalatina is synapomorphous of osteichthyans. The eye supported by the bony palatoquadrate is a teleostomian synapomorphy. Dermal elements support the eye in actinopterygians, the entopterygoid in advanced actinopterygians, but the ectopterygoid in lepisosteids.A quadratojugal is a synapomorphy of osteichthyans but exhibits a number of transformations in connection with the vertical pit-line and the preopercular canal; a quadratojugal bearing the vertical pit-line is the primitive condition for osteichthyans. Ontogenetic evidence does not support the homology of the membranous posterior process of the teleostean quadrate with the quadratojugal. The lack of a quadratojugal and the presence of the elongate posterior or posteroventral process of the quadrate is a synapomorphy of teleosts.

Notes: Rickettsiae-like structures were found in the salivary gland cells of Drosophila auraria during different larval and prepupal developmental stages, from the early 3rd instar up to 14 hr after spiracle inversion. These microorganisms are surrounded by a membrane, are constantly intracellular, and occur singly or in groups. Their widespread occurrence in various tissues of other Drosophila species indicates that they can be considered as symbionts, but their actual functional significance (if any) is unknown.

Notes: Histology of each of the five segments of the oviduct of the female turtle Chrysemys picta was described for successive intervals throughout their annual cycle. Uterine and glandular segments showed marked seasonal variations in the extent and content of the submucosal and epithelial glands. Submucosal glands were most prominent in preovulatory and postovulatory animals (May to June), regressing in late summer (oviposited animals) and recrudescing the following spring. These changes correlated with variations in the muscularis layer, the number of uterine epithelial blebs, oviductal vascularity, and the presence of eosinophils in cervical segment cross-sections. These cyclic seasonal changes are discussed in relationship to reported seasonal changes in gonadal steroids in this species. Hormonal control was corroborated by oviductal response to estradiol-17β injected (1 mg/kg daily for 2 weeks) into mature, reproductively inactive (winter) animals. This treatment induced increases in glandular activity, vascularity, and distribution of eosinophils comparable to those of reproductively active (summer) animals.

Notes: Molluscan shells, including those of Gastropoda, are formed by accretionary growth at the mantle edge. The mantle is a thin membrane of skirt-like shape, which extends minutely beyond the aperture, and its edge adds a shell increment to the aperture margin so that each increment copies a configuration of the mantle edge at that time. Thus, regulation of shell morphogeny is almost equivalent to the factors which control the mantle form at the moment of shell growth. Form of the mantle skirt is considered to be kept in a state of balance between the force of its internal stress and forces acting on it such as fluid pressure or muscle contraction.The expansion behavior of the mantle skirt has been numerically analyzed by using an elastic model (DMS-tube), which represents the fundamental structure of the mantle tissue as a double membrane structure with internal springs (DMS). Four characteristic expansion patterns of the DMS-tube have been detected: (1) general outward expansion; (2) developing a ridge-like fold on an initial longitudinal protrusion of the tube edge; (3) drastic shift of the expanded state from a uniformly curved to an elliptical shape in outline, owing to the existence of a fixed boundary condition on the tube wall; and (4) constricted protrusion on the open region of the shell wall surrounding the DMS-tube. These results have the potential for answering the following questions relating to the morphogenesis of gastropod shells. How does the mantle skirt usually make contact with the inner surface of the shell wall so as to ensure continuous accretion of shell materials to the aperture margin? What is the cause of spiral ridges? Why do open coiling or minimally overlapping shells have generally circular apertures, while shells with apertures overlapped by whorls have non-uniformly curved apertural lips? What is the cause of long closed spines and why do they always appear on spiral ridges?

Notes: The larval antenna of Bombyx mori has 13 sensilla and about 52 sensory neurons in its distal portion. The axons form two nerve cords which unite in the cranial hemocoel to supply the brain as the olfactory nerve. The antennal imaginal disc, which is a thick pseudostratified epithelium continuous with the antennal epidermis, thickens markedly during the 5th instar by rapid cell proliferation. At the prepupal stage cell proliferation ceases and the disc everts to form a large pupal antenna. Simultaneously, an extensive cell rearrangement occurs in the antennal epidermis and the disc tissue becomes much thinner because of the abrupt expansion of antennal surface area. The two larval nerve cords thin down markedly by degeneration of axons, but they do not disintegrate totally even after the onset of pupation. The epidermis of the larval antenna forms the distal portion of the pupal antenna, while the imaginal disc forms the more basal portion. Development to the adult antenna occurs almost immediately after the onset of pupation; many adult neurons appear in the simple epidermis facing toward the thick outer side of the newly formed pupal cuticle. By 12 hours after the onset of pupation, these neurons align themselves in many transverse rows which are the first sign of the adult antennal configuration. Addition of these neuronal axons to the once-thinned nerve cords causes resumed thickening of the cords during the first 24 hours and thereafter. Differentiation of adult sensilla begins in the next 24 hours and is almost completed at the third day of pupation, which requires a total of 10 days.

Notes: Sensilla diversity and abundance were extremely high on the apex of the maxillary and labial palpi of two species of Gryllacrididae. The terminal segment of the maxillary palpi of these species had 9 and 15 sensilla types, respectively, and up to 2,834 sensilla. The labial palpi had 7 and 12 types, respectively, and up to 5,195 sensilla. Several types of multiporous smooth and ridged olfactory basiconic sensilla, and coeloconic, coelosphaeric, placoid, and multipapilliform sensilla occurred, as well as many trichoid sensilla and the more typical uniporous basiconic contact receptors. Two species of the closely related Stenopelmatidae were compared to the gryllacridids and found to have similar sensillar diversity and abundance, but three species of the more distantly related Tettigoniidae had only 4 or 5 sensilla types and a total number ranging from 320 to 960 on their maxillary palpi.

Notes: The results of volumetric measurements led Hanström ('28) to suggest that specialized neuropil in the brain, the so-called central body (CB), may be of particular importance in the nervous control of web building behavior in spiders. We compared the volumes of the various brain regions in four spider species clearly differing in lifestyle and web building behavior: an orb weaver (Nephila clavipes), a wandering spider (Cupiennius salei), a jumping spider (Phidippus regius), and a bird spider (Ephebopus sp.). Our results obtained in adult animals as well as our observations on the postembryonic development of the brain do not support Hanström's hypothesis. The relative share of the CB in the brain is very similar in all four species (ca. 3.1 to 5.1%). The differentiation of the CB into a clearly demarcated two-lobed structure does not coincide with the onset of web building behavior in Nephila. The CB of both Nephila and Cupiennius is already clearly recognizable in spiderlings which have not even left the egg sac.

Notes: The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and “dark” cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and “dark” cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and “dark” cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands.Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.

Notes: The organization of identified neurosecretory cell groups in the larval brain of the tobacco hornworm, Manduca sexta, was investigated immunocytologically. Computer-assisted three-dimensional reconstruction was used to examine the architecture of the neurosecretory cell groups. The group III lateral neurosecretory cells (L-NSC III) which produce the prothoracicotropic hormone are located dorsolaterally in the protocerebrum and extend axons medially that decussate to the contralateral lobe prior to exiting the brain through the nervi corporis cardiaci I + II. The group IIa2 medial neurosecretory cells (M-NSC IIa2) are located anteriorly in the medial dorsal protocerebrum. The axons of these cells also exit the brain via the contralateral nervi corporis cardiaci I + II. However, their axons traverse a different pathway through the brain from that of the L-NSC III axons. Each of the cell groups possesses elaborate dendrites with terminal varicosities. The dendrites can be classified into specific fields based upon their location and projection pattern within the brain. The dendrites for these two neurosecretory cell groups overlap in specific regions of the protocerebral neuropil. After the axons of these neurosecretory cells exit the brain through the retrocerebral nerve, they innervate the corpus allatum where they arborize to form neurohemal terminals in strikingly different patterns. The L-NSC III penetrate throughout the glandular structure and the M-NSC IIa2 terminals are restricted to the external sheath. A third group of cerebral neurosecretory cells, the ventromedial neurons (VM) which stain with the monoclonal antibody to prothoracicotropic hormone in Manduca, are located anteriorly in the medial region of the brain. The axons of these cells do not exit the brain to the retrocerebral complex, but rather pass through the circumesophageal connectives and ventral nerve cord. These neurons appear to be the same VM neurons that produce eclosion hormone. One dendritic field of the L-NSC III terminates in close apposition to the VM neurons. The distinct morphologies of these neurosecretory cell groups in relation to other cell groups and the distribution of neuropeptides within the neurons suggest that insect neurosecretory cells, like their vertebrate counterparts, may have multiple regulatory roles.

Notes: The micropylar apparatus (MA) in Rhagoletis cerasi (Diptera, Tephritidae) is located at the anterior pole of the egg and consists of two parts: an outer chorion and an inner vitelline membrane. Sperm entry takes place through the micropylar canal, 2.0-2.5 μm in diameter, which penetrates the micropylar endochorion and terminates in the thick vitelline membrane, thus forming the “pocket.” The pore of the micropylar canal, i.e., the micropyle, is covered by the exochorionic tuft.The formation of the MA is accomplished by 40 micropylar cells during oogenesis. These cells secrete the successive eggshell layers: the vitelline membrane, the wax layer, the innermost chorionic layer, the micropylar endochorion, and the exochorion. Two among 40 micropylar cells differentiate and form two tightly connected projections. The latter contain a bundle of parallel microtubules and participate in the formation of the micropylar canal and the pocket. At the tip of the projections there are two thin extensions full of microfilaments. In late developmental stages the two projections and the extensions degenerate and leave the canal and the pocket behind. We also discuss the structural features of the MA in relation to its physiology among Diptera.

Notes: It is uncommon to find acid phosphatase activity in mature secretory granules. This paper demonstrates by light and electron microscope cytochemistry an acid phosphatase in mature secretory granules in the cells of one region of the salivary gland of Bradysia hygida (Diptera, Sciaridae). These secretory granules increase in number during larval development up to the beginning of the pre-pupal period when they undergo massive exocytosis. Biochemical assays show that upon exocytosis of the majority of the granules the total acid phosphatase activity in the granular gland region drops to 10% of the maximum reached before exocytosis. During and after exocytosis, two other acid phosphatases, eletrophoretically different and much weaker in activity, become increasingly detectable in all gland regions. At the same time, in whole mount preparations, numerous tiny acid phosphatase-positive granules (probably secondary lysosomes) become evident in all major cell types of the salivary gland. These results indicate that the S2 region of the salivary gland has mature secretory granules containing an acid phosphatase destined for exocytosis which is different in molecular properties from other acid phosphatases (likely lysosomal) made by the gland.