42 K. MITSUKURI AND 0. ISHIKAWA. 



out this idea very completely in Amphibia, and has also shown, 

 from the investigations of other workers, how the same idea 

 could be carried out through other classes of Vertebrata. We 

 need hardly say that our investigations most completely bear 

 out Balfour's and Hertwig's view. In fact, the agreement 

 between the development of Amphioxus and Amphibia on one 

 side, and of Reptilia on the other, as shown by our work, is as 

 complete as could be desired, when we make due allowance for 

 the fact that on one side is a holoblastic and on the other a 

 meroblastic egg. Let us examine more in detail. 



When we compare our fig. 16 with Hertwig^s fig. 4 (Taf. ii. 

 No. 6) of Triton, we are at once struck with the close similarity 

 between the two, allowing for the fact that the latter represents 

 a whole egg, and the former only a small part of it. There is 

 in both a passage connecting the cavity which becomes the 

 future alimentary canal with the exterior. This is, according to 

 Hertwig's nomenclature, " die enger Theil der Darmhohle 

 [dh.),'^ according to ours "the blastoporic passage.^^ At the 

 dorsal lip of this passage the ectoblast in both is reflected, and 

 becomes continuous with the chorJa-entoblast. In the region 

 in front of the passage the embryo consists of only the ectoblast 

 and entoblast. In both there is the yolk-plug behind the 

 passage, and contiguous with it the two primary layers are 

 fused, and from the fused point there stretches backward an 

 unpaired mesoblastic mass. Hertwig's fig. 11, Taf. v, and 

 figs. 7 and 10, Taf. vi, of Rana, are essentially alike. 



Hertwig's fig. 17 (Taf. iv) is the frontal section through the 

 line a — b of fig. 4, Taf. ii. It passes through the beginning of 

 the unpaired mass of mesoblast. It presents an appearance 

 very similar to our fig. 8 of the corresponding region. The 

 ectoblast is proliferating in the median line, and giving cells 

 to the mesoblast. 



In our figure the entoblast and mesoblast are separate, but 

 we have shown already that they become continuous further 

 forward. Hence exactly the same relations hold in this region 

 in Triton and Trionyx. Compare also fig. 2, Taf. vi, and fig. 5, 

 Taf. viii, given by Hertwig of the corresponding region in Rana. 



