278 PHYSIOLOGY AT THE FAEM. 



the nervous system and muscles ; whereas the glands and 

 internal organs are formed from the mucous layer, which is 

 that part of the membrane farthest removed from the action 

 of the male element." * 



The function of reproduction in birds and other vertebrated 

 animals which are viviparous, is not so different from that in 

 mammals as may at first sight appear. In all birds the male 

 organs have their place in one individual, the female organs in 

 another individual. The testes, or spermatic organs of the 

 male, are compact bodies situated close to the kidneys, com- 

 posed, as in mammals, of long convoluted tubules, and made 

 capable of great development at the season of sexual activity. 

 The seminal ducts derived from the testes terminate by two 

 distinct orifices in the cloaca, and a pair of papillary elevations 

 in which these terminate constitute in most birds the sole 

 rudiment of a penis. The ovary is, like the testes in the 

 male, situated close to the kidney, and is composed of a 

 " stroma," or bed of compact fibrous tissue, in the midst of 

 which the ova are developed. As the ovisacs enlarge, they 

 gradually project, carrying before them their envelopes, and at 

 last the ovary presents almost the appearance of a bunch of 

 grapes. At last the ovum escapes by the rupture of its cover- 

 ings, and these remain in a sort of cup, which finally disap- 

 pears by absorption. The oviduct commences by a wide slit, 

 into which the ovum, at its escape from the ovary, is received ; 

 at the lower part the oviduct dilates into a thick glandular 

 sac, which secretes the shell. It terminates in the cloaca, the 

 common outlet of the rectum, and of the genito-urinary ap- 

 paratus. What is singular is, that in most birds only one 

 ovary is developed, though in the embryo two are present ; 

 the right ovary and oviduct remain unchanged for the rest of 

 life. Hence, while there are two Fallopian tubes in mammals, 



* Bennett, ' Outlines, ' p. 164. 



