48 K. MITSUKURT. 



the aforesaid stretch (3f epithelium has been cut off from the enteric 

 cavity and incorporated with the mesoblast. 



In ti note published in the Anatomischer Anzeiger, No. 7, 1891 

 I called attention to the section o-iven iri Fig. 23 of the present paper, 

 and Fio's. 25 and 29 of our 'f rion yx paper, and pointed out that while 

 both represented essentially the same structure, mesoblast cells in Trio- 

 n y X were budded off as separate stellate cells, while those in C 1 c i ii m y s 

 appenred as a more or less solid mass. I liave now to qu.alify that 

 statement. On referring to the original sections from which Figs. 25 

 and 29 of Trionyx were drawn, i find that they are very faithful re- 

 presentations. But in sections which I have obtained lately, I find 

 that the cells appear aggregated in a. loose mass, and are by no means 

 so separate as in Figs. 25 and 29. This difference, 1 think, is due to 

 difference in the fluid in wiiich they were killed. The earlier 

 embryos were treated with corrosive sublimate, wliile the later ones were 

 all ])reserved in picro-sulphuric acid. I am now inclined to tliinkt that, 

 Trionyx and Clemmy s are after all, not so unlike in this respect. 



So far as I am aware, the facts described al)ove in regard to the 

 earlier phases in the formaticin of the gjistral mesoblast are now 

 brought out for the first time. It appears to me tliat they have 

 considerable significance, for they make the process of the mesoblast 

 formation in higher vertebrates agree with the same process in Am- 

 phioxus mneh more closely than we have hitherto been able to do. 

 These facts h;i ve also, in my opinion, an important bearing in explaining 

 the mesoblast formation in the chick. Fig. 100 in P>alfour's Comparative 

 Emhniology, A'ol. 11. is substantially the same as Fig. 17 or 38 of the 

 present paper. Balfour says : — " From wliat has just l)een said, it is 

 clear that in the region* of the embryo the mesoblast originates as two 



* I. e. in front of the primitive streak. 



