lO WALLACE. [Vol. XV. 



the extra-embryonic region the ectoderm is two cells deep, with 

 no peripheral thickening ; while in the embryonic region there 

 is a centripetal growth of cells, thickest near the margin and 

 thinning out anteriorly until some of the cells appear to be lying 

 loose on the periblastic floor. A cross-section, passing through 

 the axial thickening, shows that this tongue of cells also thins 

 out laterally (PL III, Fig. 2). Very soon after the germ-ring 

 attains its maximum development (PL II, Fig. 7) it begins 

 to decrease. This decrease is shown in an enlarged view of a 

 later stage, PL III, Fig. 9, in which the ring is narrow at the 

 anterior pole, gradually broadening toward the posterior or 

 embryonic pole. Cross-sections of the rim at the cardinal 

 points reveal an interesting modification of the germ-ring in 

 the ordinary teleostean egg. In a section at the anterior pole 

 no invagination obtains, but rather a centripetal proliferation of 

 cells from the ectoderm (PL III, Fig. 3). In Professor Wilson's 

 paper on the Sea Bass ^ he says : " The peripheral part of the 

 blastoderm, both where there is a large Randwulst and none at 

 all, is an undifferentiated area, and the germ-ring consequently 

 starts at some distance from the extreme edge of the blasto 

 derm." If we follow this interpretation of terms, we have in 

 Batrachus no germ-ring, as there is no under layer of cells dif- 

 ferentiated from the rest of the blastoderm. A section through 

 the lateral region more strongly expresses the fact that there 

 is no invagination, the blastoderm being actually thinner at the 

 periphery, as shown in PL III, Fig. 4. Here, also, we find no 

 distinct under layer, but a few loose cells which are budded off 

 centripetally from the slight peripheral thickening. As the 

 occurrence of these loose cells is constant, might they not rep- 

 resent the distinct layer found in other forms .' Passing to the 

 posterior pole, a section is shown through the longitudinal axis 

 of the embryo (PL III, Fig. 5). Here is a decidedly invagi- 

 nated appearance, but no real invagination, so far as can be 

 judged from a study of successive stages. The appearance 

 may be due to a rapid proliferation of cells both centripetally 

 and dorso-ventrally {cf. PL III, Fig. i), and also to the growth 



' Henry V. Wilson, " The Embryology of the Sea Bass (Serranus atrarius)." 

 Bulletin of the U. S. F. C, vol. i.x. For 1S89. 



