I.] THE FROG. 23 



toneum over their ventral faces. The ducts of the kidneys 

 pass along their outer edges and, approaching as they pass 

 backwards, open by two slit-like apertures in the posterior 

 wall of the cloaca. 



The urinary bladder {urocyst) is a large bilobed sac, 

 opening posteriorly, by a wide median aperture, into the 

 antero-ventral end of the cloaca. 



The testes are ovoidal yellowish bodies situated in front 

 of the kidneys and enveloped in peritoneum, a fold of which, 

 forming a sort of testicular mesentery or mesorchium, is de- 

 rived from that which covers the ventral face of the kidney. 

 The delicate vasa efferentia of the testes may be seen travers- 

 ing this fold to enter the substance of the kidney. They 

 communicate with the urinary tubules, and thus the duct of 

 the kidney serves not only as the duct of the urinary se- 

 cretion but as the vas deferens. 



The spermatozoa of the Frog are filiform bodies with 

 cylindrical, more or less linear, nucleus bearing heads. 



The ovaries are broad lamellar organs, very large and 

 much folded and plaited in the breeding season. In- 

 numerable ovisacs, or follicles, containing dark-coloured 

 ova, are scattered through the substance of the ovary and 

 give rise to projections on its surface as they become 

 fully developed. The ova are finally thrown off by 

 dehiscence. 



The oviducts are long convoluted tubes situated on each 

 side of the dorsal wall of the abdominal cavity, to which they 

 are connected by peritoneal folds; each curves over the 

 outer face of the root of the lung. Their anterior ends are 

 very slender, and terminate by open mouths at the sides of 

 the pericardium, between the attachment of the so-called 

 diaphragm and the lobe of the liver. For the greater part 

 of their length their walls are thick and glandular, and 



