FROGS AND TOADS 257 



newts, on the other hand, lost parts of the body tail, legs, eyes, etc. 

 grow again.) 



3. Mouth. (a) The tongue, which is very extensile and has two long, 

 pointed lobes behind, is used as an organ of prehension. It is fixed by 

 its anterior end to the floor of the mouth, from which it can be rapidly 

 protruded (fly-flap). 



(1} Small curved teeth are developed in the upper jaw and palate, but 

 are only used for holding the food and pushing it on towards the throat 

 (see lizard). 



E. Reproduction. 



1. About the beginning of May, with the revival of insect life, the 

 frogs emerge from the mud in which they have passed about seven 

 months of hibernation. (Why ?) At this time the warm spring nights 

 are rendered everywhere sonorous with their concerts. As among song- 

 birds, it is the male only that is vocally gifted. The sound of the voice is 

 strengthened by two vocal sacs, situated near the angles of the mouth, 

 and protruded from slits in the act of croaking. 



2. At the beginning of June the female spawns i.e., deposits its eggs. 

 Their number is large (as many as 4,000), though not excessive when we 

 consider the numerous enemies to which the frog and its young are 

 exposed, and the fact that the parents neither concern themselves about 

 the eggs or the young. 



3. The eggs, which lie in lumps at the bottom of the water, are 

 hatched by the heat of the sun transmitted through the water. They 

 have the form of small yellowish balls, and are surrounded by a trans- 

 parent, jelly-like envelope, which swells considerably in the water. 

 (Why do they not require a solid envelope?) This jelly protects the 

 eggs against injury, and also from being swallowed by fish and other 

 aquatic animals. (Why ? Only the duck can consume them by means 

 of its broad, spoon-shaped bill.) The jelly further increases the space 

 between the separate eggs (for purposes of respiration), and finally 

 constitutes the earliest nutriment of the larvae. 



F. Development. 



Observe this in an aquarium. As the larvae, or tadpoles, pass 

 through all the stages of their development in the water, they have 

 in all respects the structure of an aquatic animal. 



1. In shape they are like fish (which see) ; the head passes directly 

 into the limbless trunk, which is continued into 



2. A laterally-compressed swimming-tail, exceeding the length of the 

 body, and completely surrounded by a broad fin-membrane. The larva 



