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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 173 (1973), S. 319-332 
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dorsal (D), lateral (L and R), and ventral (V) portions of the endoderm of blastulae ofAmbystoma mexicanum of different age (stages 8+ to 10−) were combined with ectodermal caps of stage 8+ blastulae. All V and most L and R portions induced only ventrocaudal mesodermal structures — “ventral” type of mesoderm induction. Almost all D portions induced much more voluminous structures of predominantly axial character — “dorsal” type of mesoderm induction. The difference in mesoderm-inducing capacity of the dorsal as against the lateral and ventral endoderm is probably purely quantitative in character. The dorsal endoderm exhibits a pronounced dominance in mesoderm-inducing capacity. During the early symmetrization of the amphibian egg it is apparently especially the presumptive dorsal endoderm that becomes endowed with strong mesoderm-inducing properties. A comparison of the results obtained with endodermal portions of blastulae of different age showed that the mesoderm-inducing capacity first begins to decline in the dorsal endoderm (around stage 9), subsequently in the lateral, and finally in the ventral endoderm (at stage 10−). At stage 10− the dorsal endoderm no longer has mesoderm-inducing capacities. In the recombinates there is a striking correspondence between the regional differentiation of the mesoderm and that of the endoderm. The latter differs markedly from the presumptive significance of the various endodermal regions in the normal embryo. Primordial germ cells, which constitute a characteristic component of the “ventral” type of mesoderm induction, can be induced not only by ventral, but also by lateral and to some extent even by dorsal endoderm. The development of primordial germ cells from the ectodermal component of the various recombinates indicates that in the urodeles the origin of the primordial germ cells differs markedly from that in the anurans.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 181 (1977), S. 89-93 
    ISSN: 1432-041X
    Keywords: Cleavage ; Normal table ; Axolotl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Films of cleaving embryos of the axolotl,Ambystoma mexicanum, taken by the “double camera” technique, were used in order to arrive at a more detailed staging based on quantitative criteria. Drawings were made of the animal hemispheres just prior to the start of each cleavage cycle from the 6th to the 15th cleavage. The number of cells intersected either by the (apparent) “egg diameter” (up to the 10th cleavage) or by “half the diameter” (from the 10th cleavage onwards) was determined. The cell numbers for each cleavage cycle did not overlap with those of the previous or succeeding cycles. On the basis of these cell numbers, in place of the four Harrison stages 6–9, 10 successive stages were established each of which corresponds to one cleavage cycle.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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