THE OVARIAN EGG. 293 
lime to consolidate it slightly, and it forms a 
membrane; yet the white, the membrane, and 
the shell have all the same quality, except that - 
the proportion of lime is more or less in the dif 
ferent layers. 
But, as I have said, the various envelopes of 
eggs, the presence or absence of a shell, and the 
absolute size of the egg, are accessory features, 
belonging not tothe egg as egg, but to the spe- 
cial kind of being from which the egg has arisen, 
and into which it is to develop. What is common 
to all eggs and essential to them all is that which 
corresponds to the yolk in the bird’s egg. But 
their later mode of development, the degree of 
perfection acquired by the egg and germ before 
being laid, the term required for the germ to 
come to maturity,-as well as the frequency and 
regularity of the broods, are all features varying 
with the different kinds of animals. There are 
those that lay eggs once a year, at a particular 
season, and then die; so that their existence may 
be compared to that of annual plants, undergo- 
ing their natural growth in a season, to exist 
during the remainder of the year only in the 
form of an egg or seed. The majority of Insects 
belong to this category, as do also our large 
Jelly-Fishes; many others have a slow growth, 
extending over several years, during which they 
reach their maturity, and for a longer or shorter 
