Animal Life arid Intelligence. 



processes, waste and repair, are in equilibrium. In old 

 age, waste slowly but surely gains the mastery; and at 

 death the balanced process ceases, decomposition sets in, 

 and the elements of the body are scattered to the winds or 

 returned to mother earth. 



There are generally limits of growth which are not 

 exceeded by any individuals of each particular kind of 

 animal. But these limits are somewhat variable among 

 the individuals of each kind. There are big men and 

 little men, cart-horses and ponies, bloodhounds and lap- 

 dogs. Wild animals, however, when fully grown, do not 

 vary so much in size. The period of growth is also 

 variable. Many of the lower backboned animals probably 

 grow during the whole of life, but those which suckle their 

 young generally cease growing after a fraction (in us from 

 one-fourth to one-fifth) of the allotted span of life is 

 past. 



5. But animals not only grow — they also ^' grow up.'* 

 The kitten grows up into a cat, which is somewhat di£ferent 

 from the kitten. We speak of this growing up of an animal 

 as its development. The proportion of the various parts 

 and organs progressively alter. The relative lengths of 

 the arms and legs, and the relative size of the head, are 

 not the same in the infant as in the man or woman. Or, 

 take a more marked case. In early spring there is plenty 

 of frog-spawn in the ponds. A number of blackish specks 

 of the size of mustard seeds are embedded in a jelly-like 

 mass. They are frogs' eggs. They seem unorganized. 

 But watch them, and the organization will gradually 

 appear. The egg will be hatched, and give rise to a little 

 fish-like organism. This will by degrees grow into a 

 tadpole, with a powerful swimming tail and rounded head 

 and body, but with no obvious neck between them. Legs 

 will appear. The tail will shrink in size and be gradually 

 drawn into the body. The tadpole will have developed 

 into a minute frog. 



There are many of the lower animals which go through 

 a not less wonderful, if not more wonderful, metamorphosis. 



