No. I.] EMBRYOLOGY OF THE ISOPOD CRUSTACEA. 109 



are, however, numerous Crustacean ova in which such a form 

 of cleavage does occur, as, for instance, those of Ljtcifcr 

 (Brooks, '83 ), and between the holoblastic cleavage of this form 

 and a typical centrolecithal cleavage, numerous gradations are to 

 be found (see Korschelt and Heider, '91). The exact character 

 of the cleavage of the ova of the primitive Crustacea is of 

 course a matter of speculation, but the fact that centrolecithal 

 cleavage seems to be characteristic of the Crustacea, occurring 

 in practically all the groups in some grade or other, this fact 

 indicates that cases such as those of Lucifer are secondary. 

 If it be true, then, as I suppose, that all typically centrolecithal 

 ova are syncytia in the early stages of development, are we to 

 believe that with the loss of yolk and the assumption of a 

 holoblastic cleavage, all direct continuity between the spherules 

 is dissolved } Are we to believe that there is no continuity in 

 Lucifer, notwithstanding that in all probability there was con- 

 tinuity in the ova of its ancestors .-' 



In this connection the ovum of Peripatus capejisis is of no 

 little interest. It has been pointed out by Sedgwick ('86) that 

 the ova of P. Novae Zealandiae, P. capensis and P. Edivardsii 

 form a series, so far as the amount of yolk which they contain 

 is concerned, the first named having a considerable amount 

 while the last has practically none at all. Now, according to 

 the statements of Miss Sheldon ('88) the ovum of P. Novae 

 Zcalandiae undergoes a segmentation which is essentially cen- 

 trolecithal and forms a syncytium, while in P. capensis the 

 cleavage approaches the holoblastic form and yet a syncytium 

 again results. The spongy character of the capensis ovum 

 strongly suggests that the ancestors of that form possessed 

 yolk-laden ova, and that the loss of the yolk has been compara- 

 tively recent. This loss has not, however, resulted in the dis- 

 solution of the continuity of the spherules, and furnishes some 

 support for the supposition that, even in such cases as Lucifer, 

 there may be also a continuity of protoplasm, the separation 

 into distinct spherules being only apparent. 



In the ova of many Decapod Crustacea the formation of 

 what are termed yolk pyramids occurs, and it has generally 

 been supposed that the various pyramids were separated by 



