184 MANUAL OF ANIMAL BIOLOGY 



passes posteriorly from the lateral edge of each kidney and opens 

 into the cloaca. The cloaca is a common chamber into which the 

 intestinal, urinary, and genital ducts open. It is really the modi- 

 fied posterior portion of the rectum, and is present in most Ver- 

 tebrates, except in the higher Mammals. The urinary bladder 

 also opens into the cloaca opposite to the ureters. (W. fs. 107, 132.) 



The kidneys have the same structure in both sexes, but the 

 structure of the gonads as well as the arrangement of the ducts 

 are somewhat different. In the male Frog, the testes are seen 

 as a pair of small oval bodies, one attached near the anterior end 

 of each kidney. Ducts from the testes lead into the kidney ducts 

 and connect with the ureters. Thus in the male Frogs, the 

 latter serve as a common duct for both the kidney secretions 

 and the sperm, and are, therefore, designated as the urogenital 

 canals. A pair of yellowish, finger-like structures, known as the 

 fat bodies, are to be seen attached near the anterior end of each 

 testis. 



In the female Frog, lying in the same region as the testes in the 

 male, is a pair of lobulated ovaries with the fat bodies attached 

 to the anterior ends. A pair of comparatively large, white, con- 

 voluted oviducts is present, neither of which is directly attached 

 to the ovaries. Anteriorly each oviduct begins as a funnel-shaped, 

 ciliated opening situated near the anterior end of the coelom and 

 enlarges posteriorly to form a uterus which opens into the cloaca. 

 In the breeding season the ovaries are very large and fill up a great 

 portion of the body cavity. (W. f. 132.) 



D. Organ Systems 



1. Nutritive System 



The plan of structure of the alimentary canal in the Frog or in 

 any other Vertebrate is fundamentally the same as that which was 

 noted for the first time in the study of the Earthworm, and then 

 later in other of the higher Invertebrates. In all these animals, 

 stated in the simplest terms, the alimentary canal consists of a 

 tube lined with mucosa, which begins with the mouth at the 

 anterior end, runs through the body, and ends posteriorly at the 

 anal opening. This tube may be straight as in the Earthworm or 

 greatly coiled as in the Clam and, in general, in the Vertebrate 

 animals. (W. pp. 150-160.) 



