Jig WHITMAN. [Vol.1. 



So far as the published records show, Butschli is the only 

 one who has thus far undertaken to trace the origin of the 

 entoderm in Nephelis with that precision and attention to 

 details which are now required in such work. But there are 

 some important gaps in his work which must be filled before 

 the origin and relation of the germ-layers can be satisfactorily 

 determined. The posterior macromere in Clepsine, as we 

 have seen, is the sole source of the germ-bands, and its history 

 is the key to subsequent development. Unfortunately our 

 knowledge of this macromere in Nephelis is not complete 

 enough to warrant the assertion that it plays the same role ; 

 but the facts, so far as they go, point in this direction. When 

 we remember that the germ-bands of Nephelis have been 

 traced by Bergh (No. to) to ten terminal cells, which we 

 have every reason to suppose are identical with -the ten telo- 

 blasts of Clepsine, and further, that the eight-cell stage arises 

 in the same manner in both cases, it seems incredible that there 

 should be any radical differences in respect to the fate of the 

 posterior macromere. If, however, this macromere in Nephelis 

 is converted into the ten teloblasts of the germ-bands, — and there 

 is nothing against, and everything for, such a supposition, — it 

 is plain that Biitschli's observations on the origin of the germ- 

 layers are very far from complete. It is simply incredible, in 

 view of what happens in Clepsine, that the whole entoderm and 

 mesoderm should arise in the manner described by him. If the 

 deep cells discovered by Butschli represent only the earliest 

 and most anterior portion of the entoderm, then the chief diffi- 

 culty in the way of reconciling the two types of development 

 disappears. This appears to be the only mode of reconciliation 

 open to us, if my observations on Clepsine are correct ; and it 

 is entirely permissible to hold this ground until some one has 

 cleared up the history of the posterior macromere in Nephelis. 



Robin (No. 5, p. 146) attempted to do this, but his methods 

 of study were not equal to the task, and he fell into the error 

 of supposing that the products of this macromere represented 

 the dorsal moiety of the ectoderm. Biitschli has added but 

 little on this important point ; but a summary of his studies on 

 the germ-layers will be needed in order to place the subject in 

 a clear light. 



Biitschli's account begins with the eight-cell stage, with what 



