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 



