THE STUDY OF AMPHIBIANS 



127 



boys at the breeding season, a foolish and wantonly cruel 

 proceeding. 



LlFE-HlSTORY 



Pairing and Spawning. After resting throughout the winter 

 in the mud of the pond, the full-grown frogs become active 

 again as spring approaches, and they at once proceed to pair. 

 The pairing usually occurs in March in Britain, but it may be 

 earlier or later according to the 

 climate of the locality, and accord- 

 ing to the earliness or lateness 

 of the spring. The males utter 

 their familiar " grook, grook," appar- 

 ently calling to the females ; a male 

 mounts on the back of a female, 

 grasping her under the breast, helped 

 in this embrace by his swollen first 

 finger; as the eggs are passed out 

 from the female they are fertilised FIG. 39. Diagram of frog spawn 

 by microscopic sperms emitted by the s -> a " d ' oad spaw \ (T - S ' } - 



The dark spheres are the egg- 

 male ; these actively moving sperms 



bore their way through the envelope 

 of jelly surrounding the egg, and one 

 sperm enters into an intimate and 

 orderly union with each egg. 



The Eggs. The frog's egg is a 

 black sphere with a small whitish 

 spot of yolk at the lower pole. Each 

 is from 2 to 3 mm. in diameter, and 

 is surrounded by a spherical envelope 

 of jelly from 8 to 10 mm. in diameter. 

 From 1000 to 2000 or more eggs are 

 laid by one female, and they cohere 

 in large masses, which rise buoyantly 

 to the surface of the water. 



Comparison with other Eggs. The 

 frog's egg should be compared with the hen's egg. What is 

 popularly called the yolk of a hen's egg is the real ovum, an 



cells, which are surrounded by 

 spheres of jelly in the case of the 

 frog, and by a long ribbon of 

 jelly in the case of the toad. The 

 common frog may lay 1000 to 2000 

 eggs, and, as the water effects the 

 gelatinous sphere, the whole mass 

 swells up to the size of a toy 

 balloon. The diameter of each 

 sphere increases about ten times. 

 The toad may lay 2000 to 7000 eggs 

 in two strings, which may be ten 

 feet long. As the parents move 

 during the business of laying and 

 fertilising, the strings become en- 

 tangled among the water weeds. 

 In a loose part of a string float- 

 ing freely there may be three or 

 four files of eggs, on a stretched 

 part there are two files. 



