240 K. MITSUKUEI AND C. ISHIKÂWA. 



Trionyx. Compare also fig. 2, Taf. vi, and fig. 5, Taf. viii, given 

 by Hetrwig of the corresponding region in R,ana. 



Hertwig's fig. 9, Taf. ii, is the frontal section through the line 

 c — d of fig. 4, Taf. ii. It is substantially the same as om* fig. 9, 

 although there is a closer resemblance between it and our fig. 18, as 

 we have already shown. 



Unfortunately Hertwig does not give a cross section of the fi-ont 

 region of an embryo which has not yet developed the mesoblast; but 

 we are sure it will be essentially like our figs. 13 and 14, although 

 we cannot expect to find the lateral parts composed of a network of 

 cells. 



Now, as to the origin of the mesoblast, our results agree with 

 Hertwig's account as completely as could be desired. In the region 

 behind the blastopore he says the mesoblast arises as an impaired 

 mass in the Amphibia. Such is the case with Trionyx, as shown in 

 our figs. 7, 8,16, and 24. In front of the blastopore the mesoblast 

 arises as paired masses separated from each other in the median line 

 by the chorda-entoblast. For this point compare our figs. 17 and 

 20, or, best of all, figs. 25 and 29, with Hertwig's figs. 1 and 2 (Taf. 

 iii) of Triton. In the latter the chorda-entoblast passes into the 

 parietal layer of the mesoblast, while the darm-entoblast is reflected 

 just where it abuts against the chorda-entoblast, and passes into the 

 visceral layer of the mesoblast, thus constituting what amounts to a 

 pair of diverticula from the alimentaiy canal, one on each side of the 

 chorda, repeating what is seen in Amphioxus. Hertwig has marked 

 the entrance to these rudimentary diverticula with a star (*) in his 

 figures. We have also marked in our figures what we consider to be 

 the corresponding spots with the same mark (*). We think that 

 morphologists will not find any difficulty in recognising in Trionyx 

 the relations closely similar to those in Amphibia. In Trionyx the 



