MATURATION OF GAMETES 169 



bution of the ooplasm and follicle cells. The majority opinion, however, de- 

 rives the zona pellucida from the follicle cells. In addition to the zona 

 pellucida, the oocyte of the prototherian mammals has a striate layer lying 

 close to the surface of the oocyte. This striated layer probably is derived 

 from the surface ooplasm. This membrane later disappears, and a perivitelline 

 space occupies the general area between the surface of the oocyte and the 

 zona pellucida (fig. 46; Chap. 5). The zona pellucida separates from the egg 

 surface after sperm contact. 



5. Physiological Maturation of the Gametes 



a. Physiological Differentiation of the Sperm 



Added to the nuclear and cytoplasmic transformations of the sperm de- 

 scribed above, a further process of sperm ripening or maturing appears to 

 be necessary. In the mammal, for example, the sperm cell must pass through 

 the epididymis to achieve the ability to fertilize the egg. This is shown by the 

 fact that sperm taken from the seminiferous tubules will not fertilize, although, 

 morphologically, two sperm, one from the testis and one from the epididymis 

 cannot be distinguished other than by the presence in some mammals of the 

 so-called "kinoplasmic droplet" (figs. 82D, 97). These droplets do not appear 

 in great numbers upon ejaculated sperm but are found on sperm, particularly 

 in epididymides. It is possible that these droplets may arise from a secretion 

 from the epididymal cells (Collery, '44). In the dog, these droplets are at- 

 tached to the neck of the sperm in the caput epididymidis but are found at 

 the posterior end of the middle piece of the sperm in the cauda epididymidis 

 and vas deferens and are probably lost at the time of ejaculation (Collery, '44). 

 Investigators differ greatly in interpreting the significance of this body. How- 

 ever, these droplets do seem in some way to be directly or indirectly concerned 

 with the physiological maturing of the sperm. In this connection Collery ('44) 

 notes that sperm are probably motile on leaving the seminiferous tubules, but 

 active forward movement is not seen until the bead has reached the junction 

 of middle piece and tail. 



In the fowl, Domm ('30, p. 318) suggests the probability that the sperm 

 may undergo an aging or ripening process essential for reproduction some- 

 where in the reproductive system other than the seminiferous tubules. The 

 work of Lipsett quoted in Humphrey ('45) suggests that the accessory repro- 

 ductive system also is necessary for a ripening process of the sperm in urodele 

 amphibia. 



On the other hand, in the frog, sperm taken from the testis have the ability 

 to fertilize eggs. In this case, the sperm probably undergo a physiological 

 ripening in the testis along with morphological differentiation. 



The foregoing considerations suggest that a physiological maturation of 

 the sperm is necessary to enable the sperm to take part in the fertilization 

 process. 



