CHILDHOOD AND YOUTH 15 



'specific character ; they may be downy, and the down of many 

 different kinds of birds is alike ; and they may assume several 

 successive plumages, none of which are like those of the adult. 

 Although, therefore, they certainly belong to the second group of 

 young animals, the resemblance with the parents is seldom close. 

 Young birds are certainly birds, and very often the group or family 

 to which they belong can be recognised. 



When reptiles are hatched or born, they are in a much more 

 advanced state of development than occurs in the case of birds. 

 Not only is there no doubt as to their being reptiles, but they are 

 plainly crocodiles, lizards, serpents or tortoises, and although they 

 may be protected by their parents for a time, they are at once able 

 to move and to feed, and in their appearance and habits are miniature 

 copies of their own parents. ' 



The three groups into which I am placing young creatures do not 

 correspond exactly with the different classes of animals, and the 

 Batrachians (frogs, newts, toads and their allies) and the fishes 

 lie on the border-line between the second and third groups. Some 

 frogs, when they are hatched, appear as little air-breathing, terres- 

 trial creatures quite like their parents, but most pass through 

 a tadpole stage, and tadpoles not only live very different lives from 

 the adults, but differ extremely from them in appearance. So 

 also amongst fishes, some of the sharks hatch in a form so like 

 their parents that they can be at once assigned to their proper 

 family and even species, and the young stages of eels were known 

 and given separate names as different kinds of fish long before there 

 was any idea that they were young eels. 



The multitudinous tribes of animals without backbones, which, 

 in contrast with the Vertebrates (Mammals, Birds, Reptiles, 

 Batrachians and Fishes), are spoken of as Invertebrates, display 

 extremely different types of structure, but agree in usually having 

 a totally different appearance in the young and the adult stages. 

 There are some exceptions ; young spiders resemble their parents 

 in the fashion of reptiles and mammals, and here and there the 

 members of an individual family or group of invertebrates, unlike 

 their nearest relations, are hatched in a form differing from the 

 adult chiefly in size. These exceptions are usually cases of animals 

 that have taken to live in fresh water or on land, in circumstances 

 where the kind of young which is found in their nearest allies would 

 have difficulty in surviving. The nearest marine relatives of the fresh- 

 water crayfish, for instance, hatch out as delicate floating creatures 



