26 THE FROG 



its dorsal support. After the discharge of the eggs the 

 ovary becomes much reduced in size. 



(&) The oviducts, a pair of much-convoluted tubes lying 

 in the sides of the body cavity. In the breeding season they 

 become thick and glandular, furnishing the jelly which sur- 

 rounds the eggs. At its anterior end each oviduct opens, by 

 a wide funnel-shaped mouth, into the body cavity near the 

 base of the lung. Pass a bristle into the anterior end of the 

 oviduct. Posteriorly each oviduct passes into a thin-walled 

 distensible portion, the uterus; this opens into the cloaca. 

 How are the oviducts attached to the body wall ? 



C. The Peritoneum. The space between the alimentary 

 canal and the body wall is known as the coelome, or body 

 cavity, and the thin membrane which lines the body cavity 

 is the peritoneum. Near the mid-dorsal line the peri- 

 toneum is deeply infolded to surround the intestine, which 

 lies within the edge of the fold. Between the intestine and 

 the dorsal body wall the two layers of the fold are in con- 

 tact, forming the mesentery which serves to support the 

 intestine and bind the several coils together. The abdominal 

 viscera (intestine, etc.) are really outside the peritoneum 

 which forms a closed sac. Observe the peritoneal covering 

 of the pericardium, liver, gall bladder, and the vertical 

 mesentery (severed during the preliminary dissection) which 

 fastens the liver to the ventral body wall. The ovaries, 

 testes and oviducts possess special mesenteries ; examine 

 them. The bladder is attached by a short mesentery to the 

 ventral side of the rectum; notice the other mesenterial at- 

 tachment of the bladder. The lungs project from in front 

 into the body cavity and therefore possess a complete invest- 

 ment of peritoneum. The blood vessels of the viscera run 



