THE FROG 71 



Uro-genital System, 



Under the present heading two systems, the excretory and 

 reproductive, are dealt with together, not only for convenience, but 

 also because they are closely related structurally and development ally. 

 The component parts of this joint system naturally differ in the two 

 sexes, which will therefore be considered separately. The adult 

 female has the two sets of organs separate, and so presents a some- 

 what simpler condition than the male. 



The kidneys are two elongated, flat, oval structures of a 

 dark red colour, lying in the sub-vertebral lymph sinus close to the 

 vertebral column at the posterior end of the body. They are 

 actually outside the ccelom, as they are beneath the peritoneum. 

 Their inner edges are indented by a few notches and their outer 

 edges intact. On the ventral surface of each is a narrow irregular 

 strip of an orange-coloured tissue, the supra-renal body. From the 

 outer side of the kidney arises a whitish tube, the ureter, which 

 becomes free a short distance from its hinder end and runs straight 

 backwards to open into the end of the alimentary canal. The two 

 ureters open on small papillae situated close together on the dorsal 

 side of the terminal portion of the rectum, the cloaca. On the 

 ventral wall of the cloaca, immediately opposite these papillae, is the 

 single opening of the urinary bladder. The bladder is a large bilobed, 

 thin-walled sac, lying in the posterior ventral part of the body cavity. 

 These various organs together constitute the excretory system. 



The ovaries are two irregular masses, one on each side 

 immediately ventral to the kidneys. They are attached to the 

 dorsal wall of the ccelom by two folds of the peritoneum, known as 

 the mesovaria. The presence in the ovaries of a large number of 

 spherical eggs, like small shot, each half black and half white (during 

 a large part of the year) renders them very conspicuous. Each 

 egg is enclosed in a tightly fitting sac composed of a simple layer of 

 cells, and termed the follicle. To the front end of each ovary is 

 attached a number of finger-shaped lobes of yellow or orange-coloured 

 fat, these are the so-called fat bodies or corpora adiposa. A long 

 coiled tube, the oviduct, is situated laterally to the kidneys on each 

 side of the dorsal wall of the body cavity, from which it is suspended 

 by a fold of the peritoneum, the mesometrium. The front end of 

 the oviduct forms a wide funnel- shaped opening, the oviducal funnel, 

 lying far forwards dorsally to the liver. Immediately behind this 

 the duct is a slender tube, which, however, soon becomes larger, owing 

 to the fact that its walls become very glandular, and pursues a very 

 convoluted course to the level of the hinder end of the kidney. Here 

 it widens out to form a large thin- walled sac, the ovisac, which opens 



