254 GENERAL ZOOLOGY 



(Fig. 97) they are giving notice to every mature female 

 within hearing of their presence and ability to fertilize 

 eggs. 



During mating the male clasps the female with his front 

 legs and squeezes the eggs from her body. As eggs emerge, 

 sperm is discharged over them and fertilization takes place 

 in the water. The clasping reflex of the male is controlled 

 in the spinal cord and is very strong during the breeding 

 season. A male while clasping may have his head removed 

 and the whole of the body behind the front legs cut away 

 without letting go his grip; the front legs continue to hold 

 on until they die. 



The eggs of toads are laid in long strings of jelly which 

 protect them. They are usually deposited at night and a 

 single female produces from four to ten thousand each 

 spring. Tadpoles hatch from the jelly about four days 

 after the laying of the eggs. At first they have short tails 

 and a protruding yolk sac on the belly. They have no 

 mouth, but cling to aquatic vegetation by means of a 

 sucker beneath the head until the yolk is absorbed. On 

 the tenth day the mouth is well formed and the tadpoles 

 begin to feed on water plants. The gills, which are feathery 

 tufts on the sides of the head at the time of hatching, are 

 gradually covered by the backward growth of a membrane 

 (the operculum) from the head, and a well-grown tadpole 

 has only one exit for the respiratory water through a pore 

 on the left side. 



The legs grow out as little buds which later develop toes 

 at their distal ends. The front pair are formed inside the 

 opercular cavity and do not appear externally until the 

 tadpole is nearly ready to leave the water. As a tadpole 

 grows older it shows a greater fondness for animal food, 

 and the alimentary canal accordingly grows shorter. It is 

 a general rule among animals that vegetable food is associ- 

 ated with great length of digestive tract, and carnivorous 

 diet with a short enteron. The teeth in the tadpole also 

 change and the earlier chitinous exoskeletal plates associ- 



