78 THE BIOLOGY OF THE FROG CHAP. 



The walls of the body cavity and the various organs 

 contained in it are covered by a thin, moist, glistening 

 membrane, the peritoneum. This membrane is perfectly 

 continuous throughout, and is simply reflected over the 

 various organs. If we imagine that the body cavity were 

 originally empty, and that the organs it contains were 

 pushed into it from the outside, carrying the peritoneum in 



FlG. 12. Diagram of a cross section of the body of a frog showing the 

 course of the peritoneum by a dotted line, abd. v, abdominal vein ; 

 d. ao, dorsal aorta; il, ilium; inf, intestine; kd, kidney; m, m' , muscles 

 of back and abdomen respectively; mes, mesentery; p. per, p. per' , 

 parietal layer of peritoneum; pt. cv, postcaval vein; sk, skin; spy, 

 spermary or testis ; s. cu. ly. s, subcutaneous lymph sac; u. sf, urostyle ; 

 v.per, v. per', visceral peritoneum. (After Parker and Parker.) 



front of them, it will help us to understand the relation of 

 this membrane to the structures it surrounds. It is not to 

 be inferred, however, that these relations were brought 

 about in just this way, but the device will be useful in ena- 

 bling us to get the conditions clearly in mind. The alimen- 

 tary canal, the liver, the lungs, the gonads, oviducts, bladder, 

 fat bodies, and other organs are covered with peritoneum, 

 which usually adheres closely to the surface. The mesen- 



