LYMPHATIC SYSTEM 335 



portions, the nephridia (kidneys), and their ducts. The reproductive 

 organs include the gonads or sexual 'glands,' which (ovaries) pro- 

 duce the eggs or (testes) the spermatozoa, and the passages by which 

 these products are carried to the external world. To these are fre- 

 quently added accessory reproductive structures by which, in cer- 

 tain cases, the sperm is transferred to the female. 



Fig. 358. — Urogenital organs of Emys europea, after Bojanus. b, urinary bladder; 

 g, opening of vas deferens into the urogenital sinus; k, kidney; /, testis; u, ureter; vd, 

 vas deferens. 



THE EXCRETORY ORGANS 



The nephridia consist of a series of excretory tubules, specialized 

 in different ways, and of the ducts into which the tubules empty. As 

 the function of the nephridia is the elimination of the- nitrogenous 

 waste (uric acid, urea, etc.) which accumulates in the blood, they 

 ^ave an abundant blood supply, entirely derived, in the younger 

 stages of all vertebrates and in the adults of the higher groups from 

 the dorsal aorta, while in the later developmental stages and in the 

 adults of most anamniotes the aortic blood is supplemented by blood 

 coming from the tail and hind limbs by way of the caudal and iliac 

 veins (fig. 344). 



In its extreme development one of the excretory tubules may con- 

 sist of the following parts (fig. 359) : At the proximal end the tubule 

 opens into the ccelom (metacoele) by a ciliated funnel, the nephro- 

 stome; the cilia, which may continue for some distance along the 

 inside of the tubule, serving to create a current which carries the 





