BEPR OD UCTION. 445 



small size of the cells and the small chance, of every cell finding an ovum. 

 Without large numbers fertilization would not be ensured and the continu- 

 ance of the species would be endangered. 



Maturation of the Spermatozoon. — Considerable theoretical interest 

 attaches to the question of the real morphological value of the spermatozoon. 

 It is undoubtedly a cell, and has arisen by division from one of the testicular 

 cells, called the spermatocyte or sometimes the mother-cell of the spermato- 

 zoon. But is it the morphological equivalent of one of the mother-cells? 

 In most animals, and probably also in man, each spermatocyte gives rise to 

 four spermatids, which grow directly into four spermatozoa. The process of 

 derivation of the spermatozoa may be called, by analogy with the process in 

 the ripening of the ovum, maturation. The details and essence of the process 

 have been much discussed. Van Beneden found in an interesting worm, 

 Asearis, that the number of chromosomes in the nucleus of a single sperma- 

 tozoon is only half that in the original testicular cell ; that is, the process of 

 maturation of the spermatozoon consists in a reduction of the chromosomes 

 by one-half. This discovery has since been extended to many other forms, 

 including mammals and man, 1 and it has been shown further that the mature 

 spermatozoon contains only one-half of the number of chromosomes charac- 

 teristic of the tissue-cells of the species in question. In the light of the sub- 

 sequent process of fertilization these facts are interesting. Following Hert- 

 wig and Strasburger, who regard the chromatic substance of the nucleus as 

 the bearer of the hereditary qualities, many biologists now interpret this 

 halving of the chromatin as a provision for the reduction of the hered- 

 itary mass, which later will be restored to its full amount by union with 

 the egg. As we shall see, the maturation of the ovum follows a some- 

 what similar course, and. since the process has been more fully studied 

 there, we shall reserve further discussion until that subject is reached 



(p. 451). 



Semen. — Semen consists of spermatozoa, together with liquid and dissolved 

 solids, coming partly from the testes themselves, but secreted chiefly by the 

 accessory sexual glands — namely, the glands within the vasa deferentia, the 

 seminal vesicles, the prostate gland, and Cowper's glands. It is a whitish, 

 viscid, alkaline fluid, with a slight characteristic odor. The amount passed out 

 at any one time has been estimated at between 0.5 and (5 cubic centimeters. Its 

 chemical composition has not been examined exhaustively, lie-ides water, it 

 contains approximately 18 per cent, of solid substances, which comprise nuclein, 

 protamine, proteids, xanthin, lecithin, cholesterin, and other extractives. Cat, and 

 Sodium and potassium chlorides, sulphates, and phosphates. I Jnder proper treat- 

 ment colorless crystals, called Bottcher's crystals, may be obtained from semen. 

 They appear to be a phosphate of a nitrogenous base, which has been called s/),rm- 

 ine. Interest in the semen centres in its histological rather than its chemical 



features. The fluid portion serves as a vehicle for the transportation of and pos- 

 sibly also for the nutrition of the ripe spermatozoa. Colorless particles, called 



1 v. Bardeleben : loc eit. 



