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. 



Bat, 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 to the 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 



