Library

Notes: Summary 1. Volvox rotates on the longitudinal axis as it swims through the water. This is due to the fact that the flagella usually beat diagonally backward. 2. If the luminous intensity is suddenly decreased without changing the direction of the rays photopositive colonies which are oriented stop rotating and spurt directly forward. This is due to a change in the direction of the stroke of the flagella from diagonal to more nearly directly backward. 3. If the intensity is suddenly increased locomotion stops and the rate of rotation increases. This is due to a change in the direction of the stroke of the flagella from diagonal to more nearly sidewise. 4. Photonegative colonies react precisely the same as photopositive colonies except that the effects of increase and decrease in luminous intensity on the direction of the stroke of the flagella is reversed. 5. If, after either of these changes in the direction of the stroke o f the flagella has been initiated, there is no further change in the intensity of the light, the flagella continue to strike in the new direction for only 2.5 + seconds, after which they again strike in the direction which obtained before the intensity was changed. 6. If the intensity is gradually changed, there is no observable response unless the new intensity is maintained for a considerable period of time, which may result in increase or decrease in activity. 7. The eye-spots in Volvox consist of a pigment-cup, a lens which is located at the opening of the cup, and photosensitive substance which is located in the cup. There is one in each zooid, and all face outward. They are primitive eyes. 8. Orientation in photopositive colonies is due to an increase in the backward component of the stroke of the flagella on the shaded side and a decrease in this component on the opposite side. The former is due to reduction of light caused by the shadow of the pigment-cup on the photosensitive substance as the zooids are transferred from the illuminated side of the colony to the shaded side; the latter to increase of light caused by exposure of this substance as the zooids are transferred from the shaded to the illuminated side. 9. In negative colonies precisely the opposite obtains in the process of orientation. 10. Photic orientation is due to a change in the direction of the stroke of the flagella and not to change in activity. Galvanic orientation is due to decrease in activity on the side toward which the colonies turn. The processes involved are consequently not the same. 11. The orienting stimulus and the changes in the direction of the stroke of the flagella which result in orientation cease after the colonies are oriented. They remain oriented because, in the absence of external stimulation, they tend to take a straight course and because, as soon as they swerve from this course, opposite sides become unequally illuminated, resulting in change of intensity on the photosensitive substance in the eyes which leads to reorientation.

Notes: Summary 1. Volvox usually is photopositive in low and photonegative in high illumination, but the opposite obtains under certain conditions. 2. If it is dark adapted, it is always positive when exposed to light, no matter how intense, but it soon becomes negative if the light is sufficiently intense and the higher the intensity the shorter the time required. 3. If Volvox is fully adapted to any given illumination it becomes positive if the intensity is increased and negative if it is decreased, provided the change in intensity is sufficiently great and sufficiently rapid. 4. Colonies which have thus become positive remain so for a time, then they become neutral and later negative if the change of intensity is sufficiently great. The greater the change in intensity the sooner they become negative. The reverse obtains in colonies which have become negative. 5. If colonies are negative in a given luminous intensity and the intensity is momentarily reduced they become positive, remain so for a time, then become negative again. The time they remain positive varies directly with the magnitude of the reduction of the light and the time it remains reduced. The opposite obtains for colonies which are positive in a given luminous intensity. 6. Volvox may be either photopositive or photonegative in every condition of luminous intensity in which orientation occurs. 7. Darkness or reduction in luminous intensity induces changes which result in reversal from photonegative orientation in a given illumination to photopositive orientation in the same illumination, and light or increase in luminous intensity induces changes which result in the opposite. 8. If colonies are subjected to any given constant illumination, they become neutral, i. e. they become adapted to that illumination and orientation ceases. 9. Colonies which in any given illumination are not fully adapted, usually become negative if the intensity is increased and positive if it is decreased, precisely the opposite from that which obtains in colonies which are fully adapted. 10. Photopositive orientation is brought about primarily by a change in the direction of the stroke of the flagella on the shaded side of the colonies from diagonally backward to more nearly directly backward and photonegative orientation by the same change on the illuminated side. The one is due to decrease, the other to increase in the illumination of the sensitive tissue in the eyes. 11. Decrease in the illumination of the photoreceptors in colonies in the photopositive state has the same effect as increase in the illumination of the same structure in colonies in the photonegative state. 12. This difference is probably associated with the difference in the electric charge on colonies in the two states, indicated in the results presented in a subsquent paper. 13. It is assumed that response to light in Volvox is associated with photochemical changes, and an attempt has been made to account for reversal in the direction of photic orientation on the basis of postulated photochemical processes.

Notes: Summary 1. Volvox orients fairly precisely in a constant galvanic current. 2. It is positive to the cathode whenever it is photopositive and positive to the anode whenever it is photonegative. Anything which causes reversal in the direction of orientation in light causes reversal in the direction of orientation in a galvanic current, e. g. light, temperature, chemicals, hydrogen-ion concentration. 3. Galvanic orientation is due to cessation or diminution in the activity of the flagella on the side of the colony toward which it turns. Photic orientation is brought about largely, if not entirely, by change in the direction of the stroke of the flagella due to change in the amount of light received by the photosensitive tissue in the eyes, owing to rotation on the longitudinal axis. 4. When the circuit is closed the activity of the flagella in colonies which are not rotating, diminishes or ceases on the surface facing the pole toward which the colonies are positive, but the decreased activity continues only a few seconds after which the activity increases to that which obtained before the circuit was closed. If the circuit is now opened a similar response is obtained on the opposite side. 5. If the colonies are positive to the cathode the flagella on the cathode side respond after the circuit is closed and those on the anode side after it is opened. If they are positive to the anode the reverse obtains. 6. The galvanic response in the individual zooids in Volvox is only momentary. But in colonies which are swimming freely and rotating on the longitudinal axis the galvanic response on the side toward which they turn is continuous, owing to the continuous transfer of zooids to this side, from the opposite side, i. e. from the side where they are not affected by the current to the side where they are affected. 7. Reversal in the direction of galvanic orientation is probably accompanied by a change in the electric charge of the colonies. Colonies which are positive to the cathode usually drift cataphoretically toward the anode, indicating a negative charge; and those which are positive to the anode usually drift toward the cathode, indicating a positive charge. This has, however, not been unequivocally established. 8. A galvanic current induces in the lower organisms various chemical and physical changes at the anode and at the cathode surfaces but the changes induced at these two surfaces differ greatly. In some the changes at the surface toward the cathode are followed by certain conspicuous phenomena, e. g. reversal in the direction of the stroke of the cilia in Paramecium; in others those at the surface toward the anode are followed by equally conspicuous but different phenomena, e. g. contraction in Amoeba and bioluminescence in ctenophores; and in still others those on one side are followed by the same conspicuous phenomena if the organisms are in a given state, as those on the other side, if the organisms are in different state, e. g. decrease in the effectiveness of the stroke of the flagella in Volvox. 9. The reversal in galvanic response observed in Volvox is not in accord with Pflüger's law. Whether or not the responses observed on the anode side in amoeba and ctenophores also violate this law, depends upon its interpretation. 10. Galvanic stimulation in Volvox is probably associated with decrease in surface polarization and decrease in water-content.

Notes: 1Monovalent cation salts induce reversal in the direction of the stroke of the cilia; bivalent and trivalent cation salts with a few exceptions do not. Some acids induce reversal, others do not.2The duration of reversed action varies with the kind of salt and with the concentration. As the concentration increases, the duration of reversed action increases to a maximum and then decreases to zero.3Bivalent and trivalent cation salts neutralize the effect of monovalent cation salts. The relative amount required varies with the kind of salt used and with the concentration.4The amount of a given salt required to neutralize another salt is not proportional to the concentration of the salt neutralized. Weber's law does not hold.5The results seem to indicate that ciliary reversal is associated with differential adsorption and consequent changes in electric potential, but that there are also other factors involved.

Notes: Amoeba proteus contains a central elongated fluid portion (plasmasol), a rigid layer surrounding this (plasmagel), a thin elastic surface layer (plasmalemma), and a hyaline layer between the plasmagel and the plasmalemma which is fluid at the tip of active pseudopods and in certain other regions.The plasmasol is an emulsion. It consists of a fluid in which various vacuoles and granuoles are suspended. The plasmagel is probably alveolar in structure. It contains the same kinds of substances as the plasmasol, but some of the fluid appears to be gelated so as to form alveoli. The plasmalemma probably consists of interwoven protein fibers and a lipoid which fills the interstices.The plasmasol is probably hypertonic; the plasmagel and the plasmalemma are probably semipermeable. This and other factors result in an excess inflow of water, stretching the plasmagel and the plasmalemma. When a pseudopod is formed, the inner portion of the plasmagel liquefies locally. This produces a local decrease in elastic strength resulting in the formation of a protuberance, a pseudopod. As this is formed there is contraction at the posterior end, resulting in forward flow of the plasmasol and extension of the pseudopod.If the pseudopod is attached, the plasmalemma, being attached to the substratum and to the adjoining plasmagel, slides over the plasmagel above and remains stationary below, rolling movement results. If it is free, the plasmalemma is stretched out with movement in it equal on all sides. If the free pseudopods become attached to the substratum at the tip after they are thus formed, walking movement results.During locomotion of either type, the plasmasol continuously gelates at the tip of the extending pseudopods forming plasmagel, and the plasmagel continuously solates at the posterior end forming plasmasol.Response is due largely to changes in the elastic strength of the plasmagel in the adhesiveness of the plasmalemma and in turgidity.Locomotion in Amoeba verrucosa is in principle the same as it is in Amoeba proteus.