THE MALE REPRODUCTIVE ORGANS. 



861 



a schema similar to that used in the case of the ova, as follows 

 (Fig. 272). In the case of the ovum four ova are produced, but 

 only one is functional, and this one, the ripe egg, is characterized 

 by its large amount of cytoplasm, its inability to undergo further 

 cell division until fertilized, owing probably to its loss of the cen- 

 trosome, and the reduction of its chromosomes to half the num- 

 ber characteristic of the body cells of the species. In the case 

 of the spermatozoa, the four cells produced are all functional* 

 and are characterized by the practical loss of cytoplasm, reduc- 

 tion of chromosomes by one-half, and inability to multiply until 

 cell material is furnished. The two cells supplement each other, 

 therefore. Their union restores the normal number of chromo- 

 somes, part of which are now maternal and part paternal ; the egg 

 supplies the cytoplasm and the spermatozoon the centrosome, 

 the two necessary factors in cell multiplication. 



The spermatozoa are produced in enormous numbers. It is 

 calculated that at ejaculation each cubic centimeter of the liquid 

 contains from sixty to seventy 

 millions of these cells. The 

 adult ripe spermatozoon is 

 characterized as an independ- 

 ent cell by its great motility, 

 due to the cilia-like contrac- 

 tions of its tail. Its power of 

 movement or its vitality is 

 retained under favorable con- 

 ditions for very long periods. 

 The most striking instance of 

 this fact is found in the case 



of bats. In these animals copulation takes place in the fall and 

 the uterus of the female retains the spermatozoa in activity until 

 the period of ovulation in the following spring. Even in the human 

 being it is believed that the spermatozoa may exist for many days 

 in the uterus and Fallopian tubes of the female. In the semen that 

 is ejaculated during coitus the spermatozoa are mixed with the 

 secretions of the accessory reproductive glands, such as the seminal 

 vesicles, the prostate gland, and Cowper's gland. The specific in- 

 fluence of each of these secretions is not entirely understood, but 

 experiments show that in some way they are essential to or aid 

 greatly in maintaining the motility of the spermatozoa. Steinachf 

 has found, for example, that removal of the prostate gland and 



*It is an interesting fact that in some cases (bees) two kinds of spermatids 

 are formed by an unequal division of the spermatocyte, and the smaller 

 of the two is abortive, as in the case of the polar bodies of the egg. 



t See Steinach, " Archiv f. d. gesammte Physiologic," 56, 1894, and Walker, 

 "Archiv f. Anatomic u. Physiologic," 1899, p. 313. 



Primary 

 spermatocyte. 



Secondary 

 spermatocytes- 



Spermatids. 



Spermatozoa. 



Fig. 272. Schema to indicate the proc- 

 ess of maturation of the spermatozoa. 

 (Boveri). 



