20 DEGENERATION. 



the correct building-up of the pedigree of animals at 

 least (and the remarks which follow are confined to 

 that division of the organic world), is afforded by the 

 changes — the phases of development — which every 

 animal exhibits in passing from the small shapeless 

 £&& to the adult condition. The aid which we here 

 obtain depends on the following facts. Just as we 

 suppose any one animal — say a dog — to have deve- 

 loped by slow change through an immense series of 

 ancestors which become simpler and simpler as we 

 recede into the past until we reach a small shapeless 

 lump of living matter devoid of structure, so do we 

 find actually as a matter of fact, which any one can 

 see for himself, that every individual animal begins 

 its individual life as a structureless particle which is 

 thrown off from its parent, and is known as the egg-cell 

 (Fig. i). Gradually passing through a series of more 

 and more elaborated conditions of structure, that 

 ^%Z grows into the adult dog. The changes which 

 have taken countless ages in the one case, are 

 accomplished in a few weeks in the other. 



And now we have to note the important fact which 

 makes this process of development so intensely in- 

 teresting in relation to the pedigree of the animal 



