REPRODUCTIVE SYSTEM 669 



floor of the mouth at the same time raised, air is forced 

 through the glottis into the hmgs. When the pressure on 

 the hings is relaxed, and when the muscles of the sides of 

 the body contract, the air passes out. 



Excretory system. — The paired kidneys are elongated 

 organs situated dorsally and posteriorly beside the urostyle. 

 The waste products which they filter out of the blood pass 

 backward by two ureters which open separately on the 

 dorsal wall of the cloaca, and are not directly connected 

 with the bladder. The ureter or Wolffian duct is seen as 

 a white line along the outer side of each kidney ; in the 

 male it functions also as the duct of the testis. On the 

 ventral surface of each kidney is a longitudinal yellowish 

 streak, the adrenal gland, and little spots mark ciliated 

 apertures or nephrostomes, which remain as communica- 

 tions between the abdominal cavity and the renal veins, 

 though they are originally connected with the urinary 

 tubules. There are also, as in higher Vertebrates, open- 

 ings from the abdominal cavity into the lymphatic system. 



Reproductive system. — The males are distinguishable 

 from the females by the swollen cushions on the first 

 fingers. At the breeding season in spring, they trumpet to 

 their mates. The male clasps the female with his fore- 

 limbs, and retains his hold for several days, fertilising the 

 ova as they pass out into the water. 



The paired testes are oval yellowish bodies lying in front 

 of the kidneys ; the spermatozoa pass by vasa elferentia 

 through the anterior part of the kidney into the W^olffian 

 duct, which functions both as a ureter and as a vas deferens. 

 In the male of R. esculenta the vas deferens is dilated for 

 some distance after leaving the kidney ; in R. temporaria 

 it bears on the outer side near the cloaca a dilated glandular 

 mass or " seminal vesicle." In the males, rudiments of the 

 Miillerian ducts are sometimes seen. In the male toad a 

 small rudimentary ovary, known as Bidder's organ, occurs 

 at the anterior end of the testis. 



The paired ovaries when mature are large plaited organs, 

 bearing numerous follicles or sacs containing the pig- 

 mented ova. The spawn laid by a single frog may consist 

 of several thousand eggs. The ripe ova are liberated into 

 the body cavity, and moved anteriorly towards the heart. 



