282 THE OVARIAN EGG. 
pressed this great truth in the sentence so often 
quoted, —‘“‘ Omne vivum ex ovo,’ — yet he was 
not himself aware of the significance of his own 
_statement, for the existence of the Mammalian 
egg was not then dreamed of. Since then the 
discoveries of Von Baer and others have shown 
not only that the production of eggs is common 
to all living beings without exception, from the 
lowest Radiate to the highest Vertebrate, but 
that their structure is at first identical in all, 
composed of the same primitive elements, and 
undergoing exactly the same process of growth 
up to the time when they assume the special 
character peculiar to their kind. This is un- 
questionably one of the most comprehensive gen- 
eralizations of modern times. 
In common parlance, we understand by an 
egg something of the nature of a hen’s egg, a 
mass of yolk surrounded with white and enclosed 
in a shell. But to the naturalist, the envelopes 
of the egg, which vary greatly in different ani- 
mals, are mere accessories, while the true egg, 
or, as it is called, the ovarian egg, with which the 
life of every kind of living beings may begin, is 
a minute sphere, uniform in appearance through- 
out the Animal Kingdom, though its intimate 
structure is hardly to be reached even with the 
highest powers of the microscope. Some account 
of these earlier stages of growth in the egg may 
