VERTEBRATES 119 



Kidneys, a pair of elongated dark red organs, behind the 

 spleen and against the back. Note their numerous blood 

 vessels. Possibly the ureters, or urinal ducts, can be dis- 

 covered and traced to their junction with the bladder, a 

 clear membranous sac in the posterior extremity of the 

 body cavity. 



Peritoneum, a thin membrane lining the body cavity and 

 attaching the vital organs to the backbone. 



Note. — Specimens secured in late iall, winter, or early spring may 

 contain, if female, a large number of dark-colored eggs ; or if male, two 

 white testes, located near the kidneys and similar to them in form, 

 though smaller. 



Questions. 



1. Name the parts of the frog's alimentary canal. 



2. Name the glands or organs which are accessory 

 to the canal. 



3. How long is the esophagus } How does the presence 

 or absence of a neck affect the esophagus ? 



4. How does the thickness of the stomach wall compare 

 with that of the intestine, and how do you account for the 

 difference .' 



5. Measure the length of the trunk of the frog's body 

 and that of the outstretched alimentary canal. How many 

 times the length of the one is that of the other.? How 

 does this ratio compare with that of an herbivorous 

 animal ? (The sheep's food canal is about thirty-two 

 times the length of its body.) 



6. What is the color of the bile, as seen through the 

 walls of the bile sac } This color is characteristic of carniv- 

 orous animals ; in herbivorous forms it is yellow. Find its 

 color in some omnivorous form, as man. 



7. Name the organs concerned in excretion. 



