THE FROG .- VISCERA AND VASCULAR SYSTEM 67 



in some way not understood, the eggs find their way 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 Wolffian 

 ducts. 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 the hinder end the 

 duct enlarges into a sac, which at the breeding season be- 

 comes distended with eggs and occupies a great part of the 

 body cavity. At this season, which is in March, the male 

 mounts upon the back of the female, clasping her behind 

 the arms with his fore-limbs, which are provided for the purpose 

 with the pads we have already mentioned. In this position 

 the animals remain for days until the eggs are laid. As 

 the spawn passes out, the male pours his sperm over it, 

 the eggs are fertilised (p. 10), and the slimy coating they 

 have 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. 109, 487). 



