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CHAPTER IX. 

 THE DEVELOPMENT OF THE FROG. 



I. General Account. 



The frog's eggs are laid in water, usually during March or 

 the early part of April. 



During the act of oviposition, which may last several days, 

 the male frog clasps the female firmly, embracing her with his 

 arms ; and as the eggs pass out from the cloaca of the female 

 they are fertilised by spermatozoa discharged over them by the 

 male. 



The eggs, which are very numerous, are small spherical bodies 

 about 1'75 mm. in diameter; they are invested by thin coatings 

 of an albuminous substance, which swell up very greatly in the 

 water, and stick together to form the bulky masses we call 

 frog's spawn. Such spawn consists of a transparent gelatinous 

 mass, formed by the swollen albuminous matter, in which are 

 embedded the eggs : these latter appear as small round bodies, 

 each presenting a black half and a white half. 



If a number of hen's eggs were broken into a basin, care 

 being taken not to rupture the yolks, a mass would be produced 

 similar to frog's spawn : the yellow yolks corresponding to the 

 frog's eggs, and the whites or albuminous investments of the 

 yolks to the gelatinous matrix of the spawn. And just as the 

 chicken is formed from the yolk, and not from the white of a 

 hen's egg, so also is the frog developed from the egg and not 

 from the gelatinous investment. 



The frog's eggs, laid in this way and fertilised by the sperma- 

 tozoa shed over them by the male, begin to develop at once. 

 Each egg is at first spherical, but in about a week becomes ovoid 

 in shape, and then rapidly increases in length. By the tenth 

 day it is divided by slight constrictions into head, body, and 

 tail. The whole animal becomes fish-like in appearance, the 

 tail growing rapidly : two pairs of branching tufts, the externaL 



