ORGANS OF REPRODUCTION 



381 



the ova are carried into the internal openings of the oviducts. 

 These are long twisted tubes, one on each side of the body, 

 opening in front into the body cavity by a small aperture at the 

 base of the lung, and behind into the cloaca just before the opening 

 of the Wolfhan duct. The greater part of each tube is narrow and 

 glandular and secretes a slimy substance, which sets into a jelly 

 on coming into contact with water, but at its hinder end the duct 

 enlarges into a sac, which at the breeding season becomes dis- 

 tended with eggs and occupies a greater part of the body cavity. 



Fig. 297. — Diagrams of the urinary and generative organs of the frog. 



i4, Organ? of the male ; B, those of the female ; bl., bladder ; cl., cloaca ; e.s., egg sac ;f.b., fat body ; i.o.d., 

 internal opening of oviduct ; k., kidney ; k.d., kidney duct (Wolffian duct) ; od., oviduct ; ov'., ovary ; 

 sr.b., adrenal body ; t., testis ; v.eff., vasa efferentia ; ves.sem., vesicula seminalis. 



At this season, which is in March, frogs return in large numbers 

 to the ponds where they were hatched. The male recognises a 

 gravid female by her size and warty skin and mounts upon her 

 back, clasping her behind the arms with his fore-limbs, which are 

 provided for the purpose with the pads we have alread}^ mentioned. 

 In this sexual embrace, called amplexus, the animals remain 

 for days until the eggs are laid. As the spawn passes out, its 

 contact with the pelvic region of the male acts as a stimulus for 

 him to shed his sperms over it, the eggs are fertilised (p. 5), 

 and the slimy coating that each of them has acquired in the 

 oviduct swells up and sets in the water so as to form a protective 

 layer of jelly. With their subsequent history we shall deal later 

 (pp. 629-44). When the eggs have been laid the female croaks 



