308 THE RECAPITULATION THEORY 



itself a considerable quantity of nutrient matter, 

 then the period of hatching can be postponed until 

 this nutrient matter has been used up. The conse- 

 quence is that the embryo hatches at a much later 

 stage of its development, and if the amount of food 

 material is sufficient may even leave the egg in the 

 form of the parent. In such cases the earlier 

 developmental phases are often greatly condensed 

 and abbreviated ; and as the embryo does not lead 

 a free existence, and has no need to exert itself to 

 obtain food, it commonly happens that these stages 

 are passed through in a very modified form, the 

 embryo being, as in a four-day chick, in a condition 

 in which it is clearly incapable of independent 

 existence. 



The nutrition of the embryo prior to hatching is 

 most usually effected by granules of nutrient matter, 

 known as food yolk, and embedded in the proto- 

 plasm of the egg itself ; and it is on the relative 

 abundance of these granules that the size of the 

 egg chiefly depends. Large size of eggs implies 

 diminution of number of the eggs, and hence of the 

 offspring ; and it can be well understood that while 

 some species derive advantage in the struggle for 

 existence by producing the maximum number of 

 young, to others it is of greater importance that 

 the young on hatching should be of considerable 

 size and strength, and able to begin the world on 

 their own account. In other words, some animals 

 may gain by producing a large number of small 

 eggs, others by producing a smaller number of eggs 

 of larger size i.e., provided with more food yolk. 



