6 CHILDHOOD OF ANIMALS 



venient size — ^the amoeba becomes oblong in shape and then acquires 

 a kind of waist which becomes more and more slender until only a 

 string of jelly remains. Finally this string divides, and the two 

 halves become rounded again, each forming a complete amceba, 

 exactly like the parent in all respects except size, and these two 

 at once set about the pursuit of food and begin to grow. The 

 two amoebae may be called young animals in the sense that they 

 have just come into existence as new individuals, but nothing in 

 their tissues or characters distinguishes them from their parent. So 

 far as the period of youth has any interest or significance, these 

 animals escape it. Many small creatures belonging to the lowest 

 group of the animal kingdom, the Grade known as Protozoa, repro- 

 duce like amoeba by a process of simple division, and it is tempting 

 to suppose that this method is older than the more complicated 

 fashions in which most animals multiply. Even amongst Protozoa, 

 however, very many animals begin their individual lives in a form 

 unhke that of their parents, and attain the adult condition only 

 after passing through complicated changes. I am not going to 

 describe any of these here, as they show no characters of youth 

 that are not equally well displayed in animals easier to observe. I 

 wish to recall their existence, however, because it is very frequently 

 the case in the living world that simple structures and events are 

 not primitive, and it may well be that the Protozoa without a true 

 period of youth are not surviving relics of primeval life, but are 

 forms that have become simple and degenerate because of the easy 

 conditions in which they live. 



The animals in the second group will engage most of our atten- 

 tion in this book, because they include ourselves and those most 

 nearly akin to us. As their structures, habits, and dispositions 

 are not very remote from our own, they offer problems which it is 

 possible to understand, and perhaps to solve, and they give a hope 

 of interpreting our own history and of predicting, perhaps controlling, 

 our own future. They have this in common, that the young always 

 resemble the parents more or less closely. 



Amongst human beings and monkeys, the young are born in so 

 advanced a condition that we think of them as babies and not as 

 embryos. The eyes are open, the voice is lusty, the face, the hands 

 and feet, and the body generally are shapely and well formed. But 

 the senses are deficient, especially in the great apes and man. The 

 hand of a new-bom infant will close round and cling to a broom- 

 stick or any other object placed in it, almost in the automatic 



