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 Algz 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 larvee 
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 larve begin 
to move about in the jelly some three weeks after 
