No. I.] ■ GERM-LAYERS IN CLEPSINE. 121 



symmetrically placed near the middle of the lower face of 

 the egg. Behind and somewhat above them come the two 

 daughter-cells of the neuro-nephroblast. The remaining 

 three cells (not shown) lie beneath the surface, between the two 

 anterior micromeres and the two mesoblasts, and represent the 

 earliest portion of the entoderm. The embryojiic axis has 

 precisely the same relations to the primary-cleavage planes as in 

 Clepsine. 



A further confirmation of the opinion that all the essential 

 details of the second period in the egg of Clepsine repeat 

 themselves in the egg of Nephelis is found in the peculiar 

 shifting of position among the cleavage-products. Biitschli 

 (No. II, p. 242) briefly alludes to the fact that the smaller 

 cells become more or less completely imbedded in the macro- 

 meres, and a glance at his figures shows that the anterior 

 macromere passes backward between the lateral macromeres, 

 and, ultimately, takes a position at the hind end of the embryo. 

 The same movement takes place in Clepsine, only it is not 

 carried quite so far, leaving the macromere in a median ventral 

 position, stretching from end to end. 



Biitschli does not discuss the nature of the cells derived from 

 the posterior macromere, and only alludes to them in one place 

 (p. 242) as ectoderm cells. Abandoning the only clue that could 

 guide him safely through subsequent phases, his statements 

 become indefinite, if not obscure; and neither his descriptions 

 nor his figures are free from confusion. Beyond the sixteen-cell 

 stage he is not even able to say whether his figures represent 

 the upper or lower side of the &^^, or to state definitely which 

 side corresponds to the ventral or dorsal aspect of the future 

 embryo. Entoderm cells are first represented in red, then in 

 blue, and each of the three germ-layers appears in turn in red. 

 Such incongruity in diagrammatic representation can have but 

 one explanation. Allowing that it was the best that could be 

 done under the circumstances, it is obvious enough that Biitschli 

 failed to leave the subject of the germ-layers in a satisfactory 

 state, and that much remains to be done before the origin of 

 these layers is as clear in Nephelis as in Clepsine. 



The three deep cells, which are omitted in the diagrams, were 

 discovered by Biitschli, and interpreted as the " Anlage des 

 Entoderms." Their origin was not directly observed, but their 



