GENERATION AND DEVELOPMENT 693 



by shot in the ovary have frequently been found with male 

 plumage, and disease of the ovary in hens or pheasants may lead 

 to their crowing (Leeney) . 



The Spermatic Fluid is alkaline or neutral in reaction, of viscid 

 consistence, contains proteins, nuclein, lecithin, cholesterin, fat, 

 leucine, tyrosine, kreatine, inosite, sulphur, alkaline earths, 

 chloride of sodium, and phosphates. The essential element is 

 the spermatozoa, without which the fluid is not fertile. Sperma- 

 tozoa exhibit spontaneous movement, the long tail moving from 

 side to side, by which means the organism is propelled when 

 placed in the body of the female. The vitality of spermatozoa 

 under suitable conditions is considerable, and when placed in 

 the body of the female they have been found very active many 

 days after copulation. In the bat they remain alive for months, 

 and then impregnate an ovum. Colin found them active in the 

 vesiculse seminales eight days after castration. The spermatozoa 

 are readily killed by ordinary or acidulated water, glycerin, etc. 

 The spermatozoa are produced in enormous numbers ; it is 

 estimated in man that each cubic centimetre of seminal fluid 

 contains from sixty to seventy millions of cells. A mature sper- 

 matozoon under favourable conditions is active, moving about 

 rapidly in the seminal fluid by means of its long vibratile tail. 

 It is formed of a head, a middle piece or body, and a tail. The 

 head contains the nucleus ; the middle piece the all-important 

 bright spot, the centrosome ; the tail is developed to a varying 

 degree in different animals. In the horse the length of the head, 

 which is bluntly pear-shaped, is about 5 ft ;* the tail is eight or 

 nine times as long as the head. The nucleus in the head of the 

 spermatozoon is spoken of as the male pronucleus. The testicular 

 products of hybrids, such as the mule, are infertile, not on account 

 of the absence of spermatozoa, but owing to a defect in the 

 contents of the nucleus (see p. 702). 



Seminal Vesicles and Prostate. — It is not known in what way 

 the secretions of the prostate and seminal vesicles influence the 

 main secretions with which they are ejected, but it is supposed 

 they maintain or initiate the motility of the spermatozoa. The 

 vesiculse seminales are generally regarded as receptacles for the 

 seminal fluid, but there are animals, such as dogs, cats, and 

 rabbits, devoid of these reservoirs. In the hedgehog Marshallf 

 found that during sexual activity these glands enlarged enor- 

 mously, and produced a secretion devoid of spermatozoa. He 

 accordingly considers that in this, and probably other animals, 

 the vesiculae are secretory glands, contributing to the formation 

 rather than the storage of semen. The prostate of the hedgehog 

 was also found during sexual activity to take on cell and tubule 

 * /i = a micron ; TTr Vff millimetre = ^s ^ 7 inch (nearly). f Op. cit. 



