80 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



(Plate 1, Figs. 3, 4; Plate 2, Fig. 12, cl fol. pr.). Even in the 

 undifferentiated bud (Fig. 1) , there are found among the oogonia smaller 

 nuclei that will probably give rise to nuclei of follicle cells. As the 

 oogonium increases in size, these cells multiply and form a continuous 

 epithelium around it (Plate 1, Fig. 7; Plate 3, Figs. 21, 23, 13). 

 Julin ('93, pp. 106-109) states that the first follicle is composed of 

 three cells, one of which is the sister, and the others the products of 

 division of the cousin of the ovum; and also (p. 123) that the entire 

 follicle of later stages is derived from these three cells. In our species, 

 where the ovogenesis is not so rapid, and there is plenty of time for a 

 rearrangement of the cells, there is no evidence showing that the for- 

 mation of the follicle is so precise; and the fact that in one instance a 

 small ovum has been found in the follicle of an older one (Plate 3, 

 Fig. 26) seems to show that the follicle is made up from any cells that 

 happen to be in the vicinity of the growing oogonium. 



The stalks connecting the younger follicles to the germinative epithe- 

 lium and the older ones to the stalk tissue are, as has already been 

 shown, differentiations from the germinative epithelium which connect 

 with the follicle, and are not derived from a limiting epithelium of 

 the ovary. However, even before the stalk of the follicle is com- 

 pletely established the differentiation of the primitive follicle into 

 secondary follicle cells and test cells has begun. 



2. Test Cells. 



DavidofF, in studying the origin of the test cells in D. magnilarva, 

 found evaginations of the wall of the germinative vesicle, and con- 

 cluded that these are constricted off to form the vesicular structures 

 present in the cytoplasm of the ovum. These vesicles, he says, some- 

 times appear empty and sometimes have a chromatic spot within them. 

 Their peripheral membrane stains very lightly, but as they move 

 towards the periphery of the ovum, they progressively take a deeper 

 stain and develop chromatic granules until they become the fully 

 developed nuclei of the test cells. Later their cytoplasm is formed 

 from portions of the cytoplasm of the ovum. CauUery ('94, p. 600), 

 who worked on the ovogenesis of D. rosea, does not confirm Davidoff's 

 results, but says that the test cells arise from the follicular cells by 

 mitosis. He does not, however, give the evidence upon which this 

 statement is based. 



