988 THE PHYSIOLOGY OF REPRODUCTION. 



characteristics is coincident with the maturation of functional 

 activity in the generative part of the gland, and the practical indi- 

 cation of the completion of puberty is the formation of spermatozoa. 

 In Steinach's experiments these two functions of the testis were 

 separated, and puberty, so far as the development of sex character- 

 istics was concerned, was established without the production of 

 spermatozoa. It seems probable that the secretions of the inter- 

 stitial tissue begin to influence the rest of the organism some time 

 before the generative elements mature, since sexual appetite may 

 be present before puberty, and the prepubertal growth changes 

 appear gradually. The history of this tissue, moreover, is bound up 

 in some intimate way with the activity of other glands of internal 

 secretion, with the thymus, the cortical portion of the adrenal 

 gland, and particularly with the pituitary gland. It will be re- 

 membered that deficiency of the pituitary gland (posterior lobe) is 

 accompanied by a condition of sexual infantilism. 



The Properties of the Spermatozoa. The development and 

 maturation of the spermatozoa in the testis has been followed 

 successfully by histological means. The mother-cells of the sper- 

 matozoa, the spermatocytes, give rise to four daughter-cells, sper- 

 matids, each of which develops into a functional spermatozoon. 

 The process in this case is something more than mere cell division, 

 since in the spermatozoa eventually produced the number of 

 chromosomes present in the nucleus that is, the head of the sper- 

 matozoon are reduced by one-half. The process of production 

 of the spermatozoa is therefore quite analogous to the maturation 

 of the ovum during the formation of the polar bodies. The forma- 

 tion and maturation of the spermatozoa may be represented by 

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

 306) : 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, 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 nuclear material and 

 the definite stimulus that leads to multiplication. 



* 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. 



