178 



PRINCIPLES OF ANIMAL BIOLOGY 



heart and at the extreme anterior end of the coelom or body cavity. The 

 posterior end of each oviduct is transformed into a thin-walled distensible 

 bag, the uterus, which is connected by means of a narrow passage with the 

 cloaca, in the same region as the opening of the ureter. The walls of the 

 uterus and the ureter become united side by side in their lower courses, 

 but their cavities remain distinct. Eggs are released into the body 

 cavity by ruptures in the peritoneum covering the ovaries. They are 

 carried forward to the funnels of the oviducts by the general body 

 movements, assisted by pressure of the fore arms of the clasping male. 



Fig. 147.— Uriuogenital system of female (left) and male frog. Kidney at left in male 

 is in surface view, that at right dissected to show internal tubes. A, anus; BT, Bidder's 

 tube; CL, cloaca; CT, collecting tubule; CV, postcaval vein; F, funnel of oviduct; FB, fat 

 bodies; K, kidney; LI, large intestine; MD, Muellerian duct; OV, ovary; OVD, oviduct; 

 SI, small intestine; T, testes; UB, urinary bladder; UR, ureter; UT, uterus; VE, vasa 

 efferentia. 



Currents are also produced by the strong beating of the cilia which line 

 the funnels of the oviducts. These currents sweep the eggs and other 

 matter into the open funnels and down the oviducts. The remainder 

 of the path to the exterior is indicated by the structure and arrangement 

 of the organs. 



In the male frog (Fig. 147, right) the testes are connected to the 

 kidneys by means of fine ducts, the vasa efferentia. These fine ducts 

 penetrate into the kidney and open into a longitudinal canal (Bidder^s 

 canal), which is a long tube running lengthwise of each kidney near its 

 median border. Bidder's canal is connected with the lu'eter by means 

 of a series of collecting tubules into which the uriniferous tubules (page 

 135) also open. Spermatozoa in the frog must therefore pass through 

 the vasa efferentia, Bidder's canal, the collecting tubules, the ureter. 



