REPRODUCTION 621 



reduced to one half, and thus secondary spermatocytes are pro- 

 duced. These again divide to form the spermatids (fig. 235). In 

 each spermatid the nucleus elongates and passes to the attached 

 extremity, the protoplasm decreases in amount, and a long 

 cilium develops from the free end, and the spermatozoon is 

 thus pro'luced. As they develop they seem to bore into the 

 cells oi Sertoli (fig. 236), the lipoids of which probably act as 

 nutr"ont material. 



The interstitial cells of Leydig have been already described 

 (p. 606). They are very rich in phospholipins. 



III. The Secondary Sexual Organs. 

 A. In the Male. 



1. The Prostate consists of a dense framework of fibrous 

 tissue with visceral muscular fibres enclosing dense branching- 

 glands which secrete a fluid which undergoes coagulation. 

 In some animals, e.g. the guinea-pig, it is ejaculated after 

 the rest of the seminal emission and forms a plug in the 

 vagina. 



Semen. — When the testes have become active, the glands 

 of the prostate increase and produce a fluid which, with the 

 spermatozoa, forms the semen. 



2. The Penis. — This consists of erectile tissue — a dense fibrous 

 tissue filled with irregular blood spaces, into which arteries open. 

 The penis of the bull is pointed, while that of the ram terminates 

 in a filiform process. In these animals the semen is passed 

 into the mouth of the uterus. 



B. In the Female. 



1. The Fallopian Tubes. — A tube, with a trumpet-like 

 fimbriated upper end, lying close to the ovary on each 

 side, leads to the uterus. It is lined by a mucous mem- 

 brane raised into complex ridges and covered by a ciliated 

 epithelium. 



2. The Uterus is a hollow organ with a wall composed of 

 visceral muscle fibres. In the sheep and cow and bitch it con- 

 sists of two distinct cornua — in the mare of a central part. It 

 is lined by a mucous membrane, which is covered by a ciliated 

 epithelium, and in which are tubular glands that extend down 



