164 



THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



and "test" cells of the egg of Styela were ejected from the surface cytoplasm 

 at the time of ovulation (Conklin, '05). A recent view, however, maintains 

 that the test cells arise from follicle cells and come to lie in indentations of 

 the periphery of the egg outside of the thin vitelline membrane (Tucker, '42). 

 The chorion is formed by the inner layer of follicle cells and comes to lie 

 between the test cells and the inner layer of follicle cells in the mature egg 

 (fig. 91 A). At ovulation the chorion moves away from the surface of the 

 oocyte. At this time also, the test cells move outward from their indentations 

 in the peripheral ooplasm and come to lie in the perivitelline space between 

 the egg surface and the chorion (fig. 9 IB). An ooplasmic membrane which 



TH EGA FOL LI CULI 



GRANULOSA 

 MICROPYLAR CELL 



ZONA RADIATA 



YOL K 



THECA FOLLIGULI 



f^ X'^^^ /r^^J^ "^ NUCLEI OF 



GRAN ULOS A GEL LS 



-TUBULES OF 

 CAPSULAR MEMBRANE 



MICROPYLAR CELL 



s^^^^S^^^mnmm. 





T-ZONA RADIATA 



FILAMENTS 

 PROOUCED BY 

 FOLLICLE CELLSf?) 



MEMBRANE 

 ZONA RADIATA 



Fig. 93. Vitelline membranes of certain teleost fishes. (After Eigenmann. 1890.) (A) 

 Py^osteus pungtiiis. Radial section through micropyle of egg about 0.4 mm. in diameter. 

 (B) Radial section through micropyle of egg of Percu, the perch. (C) Vitelline mem- 

 branes of Fnndiilus hcterodilus about 0.8 mm. in diameter. 



