INTEODUCTION. xiii 



or orange colour, and. in some birds, become larger in the 

 pairing season ; but their use is not fully ascertained. 



The testes lie in front of the kidneys, that of the 

 left side being usually the largest. They are greatly 

 developed in size at the pairing season. Most birds have no 

 penis ; the Ostrich and a few water birds being the only 

 exceptions. Only one ovary and oviduct is developed, gene- 

 rally that on the left side ; and, when the two are present, 

 the right one is much the smaller of the two. The ovary 

 lies on the anterior and inner side of the kidney, and is 

 flat, with transverse folds in which the e2:o;3 are formed. 

 On escaping from the ovary^ the Qg^ is received by the 

 oviduct, which is wide at first, then narrow and tortuous, 

 with longitudinal folds where the white is secreted. A 

 wider part then succeeds, where the ^gg rem.ains some 

 time, and the shell is secreted. This is considered ana- 

 logous to the uterus ; and the succeeding portion, opening 

 into the cloaca, to the vagina. In a very few birds there 

 is a clitoris present in the cloaca. 



External sexual diiferences are more marked in Birds 

 than in any other vertebrate animals, the males being 

 almost universally the more highly coloured of the two. 

 Exceptions occur in PJiynchoea, (the painted Snirpe) and 

 in some species of the little Bustard-quail^ Ortygis. As 

 a creneral rule, the male is somewhat the laro;er of the 

 two ; but Birds of prey are an exception, the females in 

 this order beinor much larger than the males, the difference 

 between the sexes being much greater than in most cases 

 where the male is the larger bird. A few other birds, viz., 

 the Leek, or lesser Elorikin, the Woodcock, some of the 

 genus Turnix, Hydrophasianus, and others, exhibit the 

 same peculiarity ; and this appears to be more an individual 

 feature, than one belonging to a family or even a genus, 



