70 CONK LIN. [Vol. XIII. 



two cells into which 4d divides, and is further continued by 

 the separation of the primary mesoblasts, m^ and va?, on the 

 anterior side. At this stage there are three cells on each side 

 derived from 4d : the primary enteroblast behind, the primary 

 mesoblast in front, and a mesentoblast cell in the middle, Figs. 

 33-41. Finally the segregation is completed by the division 

 of the middle cell of the three into a secondary enteroblast 

 behind, and a mesoblastic teloblast in front, Fig. 41. This 

 final separation of the mesoblast from the entoblast does not 

 occur until there are sixty-five cells present, of which eight cells 

 are the progeny of 4d. Of these eight cells four are entero- 



/Tn'Frimary Mesoblast. 

 /" XM'e'/'^'MesobldsticTeloUdst 

 ,ME'(M)^_^ \e'5econd.^Enterobbt. 



D/ l,,^z f ^ /e2-5econdan(Enterobld5t 



"^ ^v Primary Mesoblast 



blasts and four are mesoblasts, and the latter are almost imme- 

 diately increased to six by the division of the two primary 

 mesoblasts, m^ and m^. Fig. 42. The mesoblast ceils form a 

 short band, one on each side, which extends forward almost 

 parallel with the edge of the ectoblastic plate, but entirely 

 covered by ectoblast cells ; the enteroblasts are but partially 

 covered by ectoblast until a relatively late stage. The meso- 

 blast cells are further characterized by containing no yolk, 

 while both pairs of enteroblasts contain a considerable number 

 of yolk spherules. 



This method of the separation of the mesoblast is, I believe, 

 unique, and I should be inclined on that account to doubt the 

 correctness of the description here given were it not for the 

 fact that I have followed the lineage of the cell 4d with the 



