70 J. W. JBNKINSON. 



cess in the bat. Judging from what I know to be the effect 

 of picro-sulphuric acid upon delicate blastocysts^ I should 

 think it quite possible that Lis " blastopore " is an artifact. 

 But, apart from this, there is a very serious gap in his series 

 at what is, for his theory, the most critical point; for he has 

 no embryos whatever between the stage in which the inner 

 mass is still several cells deep, at the point of its original 

 attachment to the outer layer, which is everywhere composed 

 of a single layer of cells, and the stage in which, as he inter- 

 prets it, the inner mass has completely spread out as a single 

 layer, while the cells of the outer layer have at one point 

 proliferated to form the " amniotic mass." The cells of the 

 inner layer are at this point, as he admits, closely related to 

 those of the '^ amniotic mass " (he homologises this fusion 

 with the primitive streak), and taking into consideration 

 what we have seen of his description of a similar stage in 

 the mouse, together with the absence of the hypothetical 

 stage (fig. F), in which the cells of the outer layer and 

 those of the inner mass are alike disposed in a single layer, 

 it does not seem impossible that Duval's interpretation may 

 here also be at fault. But, whether the bat differs from 

 most other mammals in this respect or not, it seems a little 

 hazardous to suppose that other authors have misinterpreted 

 the phenomena observed by them in such different mammals 

 as Talpa, Tupaia, Sorex, Lepus, Mus, Cavia, and — since 

 Duval wrote — Tarsius, Ovis, and Sus. 



It is not necessai'y to criticise in detail Duval's attempt to 

 interpolate a hypothetical ''stade didei'mique primitif," not 

 observed even by himself in Vespertilio, among the stages 

 figured by these writers, because any one who will take the 

 trouble to look at these figures and descriptions (Heape, 13, 

 14; Hubrecht, 15—19; Assheton, 2, 3; Selenka, 27—30) 

 will be able to convince himself that Duval's interpretation 

 of their facts is exceedingly strained. Indeed, Assheton has 

 a.lready expressed his opinion that such a stage could hardly 

 have been ovei'looked by the many investigators who have 

 worked on the rabbit ; and as far as Mus, Sorex, Tupaia, and 



