82 CHILD. [VOL. I. 



circles of cilia instead of complete ones, but in only one case, 

 and then indefinitely, does he give the number of ciliated cells. 

 In no case were mesoblast-bands formed, even where they might 

 be expected. This early death shows at any rate the extreme 

 dependence of one portion of the embryo upon another. 



Finally, and this is the crucial point, from a study of his 

 paper it appears that " regeneration ' has in most cases 

 actually occurred. In no single instance does the partial larva 

 retain the form which the part would have in the whole, 

 though doubtless this is due in part to the rounding out of 

 cells in consequence of the absence of external pressure. 

 But the ectomeres always become more or less changed. They 

 form a rounded cap, not a half or a quarter of such a cap. 

 Lastly the ectomeres or cells which, in the normal cleavage, 

 come to cover the outer side of half the entomeres, in the half 

 embryo, completely overgrow tliese entomeres, tints forming a 

 gastrula and bringing the blastoporc to closure. In his descrip- 

 tion of the half embryos Crampton says: " Ectomeric divisions 

 continue, the ectodermic cap grows lower, as shown in Fig. 18, 

 before another division of A and B takes place. After the 

 fourth division of these viewed from the lower pole there are 

 four cells easily recognizable as entodermic. These are finally 

 completely overgrown by the ectodermic cells, and in one 

 case, sixteen hours after isolation, a partial circle of cilia was 

 developed." Again, in speaking of the % blastomeres, he 

 says : " Throughout later development, two large cells contain- 

 ing yolk matter are plainly seen, inclosed by the clear ecto- 

 dermic cells." Still again, in another embryo of the same 

 sort: "The two entomeres are still distinctly visible, sur- 

 rounded by ectoderm cells." In his figures the same point is 

 shown several times. 



Now, in order to accomplish this complete overgrowth and 

 inclosure of the entomeres, either the ectodermal cells have 

 changed their method of cleavage and come to*lie where nor- 

 mally they would not, or else more cells than the normal num- 

 ber have arisen from the macromeres. 



Unfortunately, only the most general statements are given 

 regarding the later development, but in any case the larvae are 



