INNER FOLLICULAR 

 E PI T H E LI UM 



OOPLASMIC MEMBRANE 



PERIVITELLINE SPACE '^C 



Fig. 91. Formation of the chorion in the egg of Styela. (A) Chorion is shown along 

 the inner aspect of the follicular epithelium. The test cells lie in indentations of the 

 peripheral ooplasm. (B) Optical section of an ovulated egg. (Redrawn and modified 

 from Tucker, '42.) 



^='1 



©mo^ 



ffi^jjg "^ 



FOLLICU L A R 

 E PITHE LIU M 



VITELLINE 

 ME MBRAN E 



ZONA R A Dl ATA 



YOLK 



^ C^C^^^-^ SECONDARY 



>/ FOLLIC U LAR 

 EPITHELIUM 



FOLLICULAR 

 EPITHELIUM 



VI TELL I N E 

 MEMBRANE 



YOLK 



D. 



Fig. 92. Developing vitelline membranes of Scyllium canicula. Observe that two mem- 

 branes are present in the young egg; later these membranes fuse into one membrane. 

 (A) Surface area of young oocyte with a vitelline membrane and zona radiata. (B) 

 Slightly older oocyte with the radiate zone not as prominent. (C) Older oocyte with a 

 single, relatively thick, vitelline membrane. (D) Nearly mature oocyte with a thin 

 vitelline membrane. (After Balfour, Plate 25, The Works of Francis Maitland Balfour, 

 ed. by Foster and Sedgwick, London, Macmillan, 1885.) 



163 



