Introductory Note to Mr. Winslow's Paper. 



[This paper is a desirable contribution to the literature 

 of embryology, inasmuch as the observer has been able 

 to follow the development of Ostrea edulis from its ear- 

 liest phases, which has never been done before by any 

 embryologist, although the artificial impregnation of the 

 eggs was attempted by M. Davaine, who says he failed, 

 and that the eggs soon became putrid and the water con- 

 taining them swarmed with infusoria. M. Davaine' s 

 figures bear the marks of having been carefully made 

 from close observations, but he obtained his material 

 from the upper gill chamber, where the ova had already 

 undergone all the changes represented from Figs. 1 to 16 

 of Brook' s drawings of the early stages of the American 

 species. Many things have accordingly escaped the 

 notice of the French author, who did not see the ' 'polar 

 globules ;' ' the first and second periods of rest and activity 

 at all. He also failed to recognize in the embryos with 

 the dorsal saddle-like depression, a blastopore stage and 

 the epibolic invagination of the hypoblast. He, however, 

 finds that the shell originates in the position of the blas- 

 topore, as shown by Brooks. He states that the velum 

 atrophies with the development of the mantle and gills, 

 but does not describe the latter. He does not note the 

 presence of a membrane around the ovarian Qgg^ and it 

 seems to me the membrane is a continuation of the vitel- 

 line, which forms a stalk by which the ovum is attached 

 to the walls of the follicles of the ovary, making a chan- 

 nel for the passage of plasma for the growth of the ovum, 

 as suggested by Balfour. 



