50 SECRETS OF ANIMAL LIFE 



female's skin also changes, and she puts on here 

 and there an adornment of pinhead-like pearls of a 

 white or pale-reddish color. In some cases the 

 pairing is fatal to the females; in some cases the 

 grass-frogs burrow into the mud after the spawning 

 is over, and rest for about a fortnight before they 

 leave for the summer-quarters. 



The globes of jelly surrounding the frog's ova 

 (one female may lay two thousand) correspond to 

 the white of egg in a hen's egg, and serve many 

 useful purposes. To begin with, the masses of 

 spawn sink or tend to sink to the floor of the pool; 

 but the spheres of jelly swell rapidly, some bubbles 

 of gas (probably oxygen from adjacent submerged 

 plants) help to buoy them up, and the clumps rise 

 to the surface. The spheres of jelly form elastic 

 cushions round the developing eggs; their un- 

 palatability and slipperiness save the embryos from 

 their enemies; they lessen the risks of drought; 

 perhaps each crystal globe acts like a little glass 

 house. In the interstices between the spheres there 

 are often minute green Algae which give off oxygen 

 in the sunlight and thus have a useful aerating 

 function. There is also a micro-fauna of frog's 

 spawn, and some of the associated little creatures 

 are of service in loosening the jelly when the larvae 

 are ready to escape. The dark pigment in the upper 

 hemisphere of the egg seems of use in absorbing 

 heat-rays, and in ordinary cases the larvae begin 

 to move about in the jelly some three weeks after 



