416 BULLETIN OF THE 



Robin ('62, '62^ "/) deserves great credit for having a long time ago 

 called especial attention to the changes which the egg undergoes previous 

 to cleavage. The changes within the cell were, however, incompletely 

 observed, and, though still (1875) maintained, in many particulars funda- 

 mentally wrong. In his more recent memoir on the development of the 

 Hirudinea, Robin ('75, pp. 26-79) has reproduced with slight additions 

 these earlier papers. The description in the one on the formation of the 

 polar globules is of particular interest, as it contains an allusion to a phe- 

 nomenon occasionally seen in Limax, but not hitherto noticed in other 

 animals. Robin says ('62^ p. 156, Fig. 8, and '75, p. 35, Fig. 10), in 

 describing the formation of the first polar globule in Nephelis : " At the 

 same time (i. e. during the constriction which rounds oft' the polar globule) 

 the clear space of the vitelline mass diminishes more and more, until the 

 separation is complete, or a plane of division is produced at the junction 

 of the vitellus and the part which is narrowed into the form of a pedicel. 

 This plane of division presents the aspect of a slender grayish or blackish 

 transverse line, and establishes a complete separation between the vitel- 

 lus and its prolongation, which then constitutes a distinct polar globule." 

 Although this plane does not (in his figures) quite correspond in position 

 to that which in Limax I have ventured to call the cell plate, I have 

 little doubt that it is really the same thing. It seems also in Nephelis 

 to be only an occasional method of finally terminating the direct connec- 

 tion of yolk and polar globule. 



Robin has in his recent work ('75, pp. 97-105) given a detailed ac- 

 count of the changes which accompany the formation of " polar rings " 

 in Clepsine, or of such as can be seen on living eggs. As this does not 

 very essentially differ from the account given by Whitman ('78"), I omit 

 a review till it can be given in connection with the observations made 

 by Whitman on the accompanying internal changes. 



The first chapter of Balfour's ('76, pp. 378-387, PL XV. Fig. 1, and 

 '78, pp. 1-9, PI. I. Fig. 1) Development of Elasmobranch Fishes is de- 

 voted to the ripe ovarian ovum. Here he concludes that observations 

 in the case of Raja batis, as far as they go, tend to show that the thick 

 membrane of the germinative vesicle is expelled, but that the contents 

 of the vesicle become mingled w^ith the surrounding yolk. He explains 

 (p. 8) how, under certain assumptions, a " consistent account of the be- 

 havior of the germinative vesicle throughout the animal kingdom " may 

 be framed. *' The germinative vesicle, usually before, but sometimes im- 

 mediately after impi-egnation, undergoes atrophy, and its contents become 

 indistinguishable from the remainder of the egg. In those cases in 



