54 PHYSIOLOGY OF THE EGGS 
eggs emerge at fifty-nine degrees lower than is 
required for the development of birds, what difficulty 
can we have in believing that at thirteen degrees less 
than the freezing point, other animals are capable of 
being hatched? Nor should I be surprised at being 
told, that there are animals whose eggs would hatch 
in a much greater degree of cold, after being aware 
that there are plants, which are beings'so similar to 
animals, that flourish amidst the regions of winter, 
and even fructify.” : 
From the experiments of John Hunter, we find that 
a hen’s egg will freeze by a great degree of cold, 
while, at the same time, it is possessed of a principle 
of vitality which prevents its destruction ; but, if 
once that principle is destroyed, cold operates on it 
more easily. He mentions that an egg was frozen 
by the cold of zero. After it was thawed, and again 
exposed to the same depth of cold, it froze seven 
minutes and a half sooner. A new laid egg took an 
hour to freeze in fifteen and seventeen degrees ; but 
when again exposed, it froze in twenty-five degrees, 
in half that time.* 
With all these facts before us, we are warranted in 
coming to the conclusion, that cold does not destroy 
the vital principle in the eggs of insects ; and it has 
been often noticed that, after a severe winter, insects 
were more numerous in the succeeding spring and 
summer. 
* See Hunter on the Animal Economy. 
