CLASS AMPHIBIA 



541 



bercles. The inner of these is large and has a homy black edge which 



is used in digging when the toad burrows into the ground. The 



other metatarsal tubercle is small. 



The toad, like the frog, has four fingers on each hand and five 



toes on each foot. The first finger is slightly longer than the 



second. 



Internal Structure 



The internal organs of the toad are similar to those of the frog, 

 and the previous description of these is referred to. Only striking 

 differences will be pointed out. The word ''frog" used subsequently 

 refers to bullfrogs or leopard frogs. 



Respiratory and Digestive Organs 



Since the toad is terrestrial and has a thicker epidermis than the 

 frog, it needs to depend to a larger extent on its lungs; these are 

 large and well vascularized, being more spongy than those of the 

 bullfrog or leopard frog. 



The motith is large and toothless, lacking the maxillary and vo- 

 merine teeth of the frog. Two openings, one on each side of the 

 tongue, are apertures to the single vocal sac. The tongue of the toad 

 is not notched behind like that of the frog. It is thicker and 

 rounded with more of its posterior end free. The surface of the 

 tongue is sticky and holds the captured insect as it is pulled back 

 into the mouth. The liver is two lobed, in contrast to the three- 

 lobed liver of the frog. 



Urinogenital Organs 



The mesonephric ducts from the kidneys, which in the frog opened 

 separately into the cloaca, unite in the toad and open into it in a 

 single duet. The urinary bladder in the toad is large and may 

 function also as a reservoir for water to prevent the animal's dry- 

 ing out. It is held in place by sheets of peritoneum and has a 

 sphincter muscle at its mouth which permits its contents to be 

 emptied rapidly. This discharge may lighten the toad and make 

 it easier to escape from its enemies. 



The testes of the toad are elongated and extend along a good 

 portion of the length of the kidney. At their anterior ends, between 

 them and the fat bodies, occurs an irregularly shaped granular 



