AVES. 251 



in a glomerulus-containing Bowman's capsule, which passes into 

 a dilated glandular portion, that, after a somewhat convoluted 

 course, is succeeded by a narrow looped part. The terminal 

 portions of the tubules form the ureter by successive unions. 



The water and salts are strained off in Bowman's capsules, 

 while the nitrogenous waste is excreted, mainly as uric acid 

 (C 5 H 4 N 4 8 ) by the glandular parts of the uriniferous tubules. 

 The urine is semi-solid. 



Male Reproductive Organs (Figs. TO and 71). The sper- 

 maries (testes) are two oval, whitish bodies, situated ventral to 

 the kidneys, and near their anterior ends. They are invested 

 and held in place by folds of peritoneum (mesorchia). From the 

 inner side of each an opaque white tube, the spermiduct (vas 

 deferens), repeatedly and sharply bent from side to side, runs on 

 the outer side of the corresponding ureter to the cloaca, dilating 

 at its end into a vesicula seminalis, and opening on a small genital 

 papilla placed just external to the opening of the ureter. 



The spermaries are made up of a large number of much- 

 convoluted seminiferous tubules formed by the continued branch- 

 ing of the spermiduct. The tubules are lined by epithelium, 

 many of the cells of which are sperm-mother-cells, producing 

 sperms (spermatozoa), with cylindrical heads and motile tails. 



Female Reproductive Organs (Fig. 71). These are only 

 developed on the left side. The ovary is a very irregular body 

 (similarly situated to the spermaries), from the outer surface of 

 which globular ova of various sizes project, enclosed in follicles. 

 It is covered by peritoneum, which forms a suspensory fold 

 (mesovarium). The oviduct is a thick- walled convoluted tube, 

 communicating with the body-cavity at one end by a delicate 

 membranous funnel situated near the, ovary, and at the other 

 entering the cloaca by a large aperture external to the opening 

 of the left ureter. The right oviduct may be represented by a 

 short blind tube having a similar situation. 



The cloaca is larger in the female. 



The ovary consists of a connective-tissue framework, the stroma, 

 richly supplied with blood-vessels. The ova are contained in 

 ovarian follicles, lined by follicular epithelium, which is again in- 

 vested by the stroma. 



These ovarian ova are, when ripe, yellow spheres rather less than 

 an inch in diameter. Such an ovum (cf. Fig. 73) is covered by 



