168 



THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



Kl NOPL A S M 1 C 

 DROPLET 



D. 



Fig. 97. Kinoplasmic bead or droplet upon the middle piece of mammalian sperm. 



(A) Pig sperm. (After Retzius, Biol. Untersuchungen, New Series, 10; Stockholm: Jena.) 



(B) Cat sperm. (After Retzius, Biol. Untersuchungen, New Series, 10; Stockholm: Jena.) 

 (C-D) Dog sperm. (C) Upper part of epididymis. (D) Lower or caudal part of 

 epididymis. 



When the vitelHne membrane thickens, the loci where the cytoplasmic strands 

 from the follicle cells pass through the membrane become little canals or 

 canaliculi. As the oocyte increases in size, a thin space forms between the 

 vitelline membrane or zona radiata and the follicle cells; it is filled with fluid 

 and forms the follicular space. The egg now is free to rotate within the follicle. 

 In consequence, the pole of the egg containing the blastodisc always appears 

 uppermost. Due to the increasing pendency of the egg follicle as the egg ma- 

 tures, the blastodisc comes to rest, a short while previous to ovulation, at the 

 base of the pedicle where the blood vessels are most abundant (fig. 47B). 

 During the latter phases of oocyte development, the vitelline membrane con- 

 stitutes an osmotic membrane through which all nourishment must pass to 

 the oocyte, particularly in its later stages of growth. The surface ooplasm forms 

 a delicate surface membrane beneath the zona radiata. 



h) Membranes of the Mammalian Oocyte. All mammalian oocytes 

 possess a membrane known as the zona pellucida. It is a homogeneous layer 

 interposed between the ooplasm and the follicle cells. By some investigators 

 it is regarded as a product of the oocyte, while others regard it as a contri- 



