THE GENERATIVE ORGANS. 251 



between the sternum and the vertebral column. The respiratory 

 movements are therefore mainly effected by the sternocostal mus- 

 cles and the elevators of the ribs, which function as inspiratory 

 muscles. 



The generative organs closely resemble those of the Reptilia. The 

 males are distinguished, not only by their superior strength, but 

 also by the brighter colour of their plumage and the greater variety 

 of their song. There are two oval testes on the anterior side of the 

 kidneys; they become much enlarged at the breeding season, and 

 the left is usually the larger. The epididymis, which is but little 

 developed, leads into the vas deferens, which passes back along the 

 outside of the ureter. The ends of the vasa deferentia are frequently 

 swollen so as to form seminal vesicles, and open on two conical 

 papillae placed on the hinder (dorsal) wall of the cloaca. 



A copulatory organ is, as a rule, wanting ; in some of the larger 

 water birds, however (Ciconia, Platalea, etc.) a rudimentary penis is 

 present as a wart-like process on the front (ventral) wall of the 

 cloaca. It is larger in most of the Struthionidce, the Ducks, Geese, 

 Swans, and in the Curassows and Guans (Penelope, Urax, Crax). In 

 these Birds a curved tube, supported by two fibrous bodies, is 

 attached to the ventral wall of the cloaca. The end of the tube can be 

 retracted by an elastic band. A superficial groove serves to conduct 

 the sperm during copulation. In the two-toed Ostrich, the penis 

 attains a still higher structure, analagous to that of the male copula- 

 tory parts of the Chelonia and Crocodilia. Below the two fibrous 

 bodies, the broad bases of which arise from the front wall of the 

 cloaca, there is a third cavernous body the extremity of which is non- 

 retractile and passes into an erectile bulb the rudiment of a glans 

 penis. 



In the female generative organs the ovary and oviduct of the right 

 side are reduced or entirely absent. The generative organs of the 

 left side, however, are correspondingly larger at the breeding season. 

 The ovary is racemose ; the oviduct is much coiled, and is divided 

 into three regions: (1) The wide abdominal ostium in front; (2) 

 the coiled glandular part which secretes, from the glands of its longi- 

 tudinally folded mucous membrane, the albumen which is added in 

 layers and is twisted together at the ends to form the chalazce ; (3) 

 a posterior short and wide portion the so-called uterus which 

 serves to produce the variously coloured egg-shell, and opens by a 

 short and narrow terminal region into the cloaca on the outer side 

 of the corresponding ureter. When there are copulatory parts in 



