2o8 THE INFANCY OF ANIMALS 



wits. The children of the impecunious, on the other 

 hand, are launched upon the world at the earliest possible 

 moment to hawk matches or newspapers in the streets. 

 There is one material difference, however, between the 

 offspring of the impecunious members of the human 

 race and the offspring of animals of limited resources : 

 and this lies in the fact that in the latter cases the 

 young, though driven to fend for themselves while still 

 exceedingly frail, are always sent out into the world 

 with a sufficiency of food to last them till they can 

 feed themselves. 



Among fishes, as with all the groups of animals so far 

 discussed, this matter of food during the early stages of 

 development varies enormously in its amount : as a conse- 

 quence we find, as usual, that there is no hard-and-fast 

 line to be drawn between embryonic and post-embryonic 

 stages, between larval and post-larval life. The members 

 of the shark tribe well illustrate this. 



As with the reptiles, some are viviparous, some undergo 

 development within eggs bountifully supplied with yolk, 

 while others are less well provided for. Since the vivi- 

 parous condition has almost certainly been evolved from 

 the oviparous, we propose to survey the latter first. 



As with the reptiles, some undergo a more or less pro- 

 longed period of development within the body of the 

 parent — of which more must be said presently : some 

 are hatched from eggs of curious shape. As a rule, both 

 with ovo-viviparous and oviparous types the growing 

 body draws its sustenance from a generous store of yolk. 

 The basking shark (Lamargus) affords an interesting 

 exception to the rule, since the young of this species are 

 hatched from exceedingly small eggs deposited, without 

 any protecting case or shell, on the sea-bottom. And 



