44 K. MITSDKDRI AND 0. ISHIKAWA. 



found in Triton and in Amphioxus. We think our figs. 25 

 and 29 ought to convince the most sceptical on this point. It is 

 significant that at one time (fig. 17) the chorda-entoblast occu- 

 pies a recess of the alimentary canal by itself, and from the 

 two sides of this recess the mesoblastic masses stretch out — a 

 relation which recalls vividly the development of Amphioxus. 



Our fig. 19 may prove a stumbling block to some in the way 

 of comparison with Amphibia. But we think this figure is 

 soon reduced to the general rule. We have already pointed 

 out that the cells forming the floor of the blastoporic passage 

 in this figure are different from those of the roof and the sides. 

 If we consider the chorda-entoblast as extending on each side 

 to the spot marked with the star, and this spot as corresponding 

 with the similarly marked spot in fig. 15, Taf. iv, of Hertwig, 

 which passes through the corresponding part of Triton, the 

 comparison will become easy. The apparent difficulty is 

 brought about by the cells of the floor being many layered in 

 Trionyx. 



There is another point on which we wish to touch. Although 

 there is no doubt that the mesoblastic masses arise as what 

 morphologically amount to diverticula of the alimentary canal, 

 the development in Trionyx has so far changed from the primi- 

 tive method that the masses no longer form an epithelium as 

 in Amphioxus or Triton or even compact masses throughout, 

 but at places only loose masses of spindle and stellate cells 

 (figs. 25 and 29). This fact will, we think, answer Kolliker's 

 objection, based upon the shape of cells in the mesoblast, 

 against the epithelial origin of the mesoblast. (We have 

 not access to Kolliker's original paper but take his views as 

 given in Hertwig's paper. No. 6, p. 105). KoUiker is no doubt 

 correct in supposing that such forms are due to very rapid 

 proliferation. 



As to the formation of the chorda, it is only necessaiy to 

 compare our figs. 25 — 28 with Hertwig's figs. 3 — 6 (Taf. iii) 

 of Triton, and figs. 8 — 11 (Taf. viii) of Rana, in order to be 

 convinced of the similarity of the process in Reptilia and 

 Amphibia. Our figs. 25 and 29 correspond with figs. 1 or 2 



