56 Animal Life and Intelligence. 



stuff for its nutrition. And this is effected, among different 

 animals, in one of three ways. Either the embryo becomes 

 at a very early stage a little, active, voracious, free- 

 swimming larva, obtaining for itself in these early days of 

 life its own living; as is the case, for example, with the 

 oyster or the star-fish. Or the ^gg from which it is de- 

 veloped contains a large store of food-yolk, on which it can 

 draw without stint ; as is the case with birds. Or else the 

 embryo becomes attached to the maternal organism in 

 such a way that it can draw on her for all the nutriment 

 which it may require; as is the case with the higher 

 mammals. 



In both these latter cases the food-material is drawn 

 from the maternal organism, and is the result of parental 

 sacrifice ; but in different ways. In the case of the bird, 

 the protoplasm of the ovum has acquired the power of 

 storing up the by-products of its vital activity. The ovum 

 of such an animal seems at first sight a standing contra- 

 diction to the statement, made some pages back, that the 

 cell cannot grow to any great extent without undergoing 

 division or fission ; and this because volume tends to outrun 

 surface. Eor the yolk of a bird's egg is a single cell, and 

 is often of large size. But when we come to examine care- 

 fully these exceptional cases of very large cells — for what 

 we call the yolk of an egg is, I repeat, composed of a single 

 cell — we find that the formative protoplasm is arranged as 

 a thin patch on one side of the yolk in the case of the 

 bird's egg, or as a thin pellicle surrounding the yolk in the 

 case of that of the lobster or the insect. All the rest is a 

 product of protoplasmic life stowed away beneath the patch 

 or within the pellicle. And this stored material is relatively 

 stable and inert, not undergoing those vital disruptive 

 changes which are characteristic of living formative proto- 

 plasm. The mass of formative protoplasm, even in the 

 large eggs of birds, is not very great, and is so arranged 

 as to offer a relatively extensive surface. All the rest, the 

 main mass of the visible egg-yolk, is the stored product of 

 a specialized activity of the formative protoplasm. But all 



