4o6 THE WONDER OF LIFE 



pelagic stage is utterly difierent from the adult type. 

 After developing for a while on a hne of its own, suited to 

 pelagic life, it begins again, as it were, on a new tack, and 

 the development is strikingly circuitous (Figs. 69, 70). 

 Many a yoimg animal received a name of its own, before 

 zoologists recognized its beginning or its end. Thus the 

 knife-blade-Kke stage in the life-history of eels was called 

 Leptocephalus. 



The third group, according to Chalmers Mitchell, includes 

 those animals which have no youth, and these he illustrates 

 by simple creatures hke Amcebse. In such cases the unit 

 which starts on an individual hfe of its own is already 

 perfect ; it does not differ in protoplasmic organization 

 from the parent cell from which it was derived. We are 

 inchned to think that it would be equally accurate to 

 say that these simple creatures never grow up, remaining 

 eternally young. Ageing began when a body began. 



When we think over our experiences of yormg animals, 

 a number of lasting impressions assert themselves. There 

 is the extraordinary abundance of hfe, the multitudes of 

 ' water-babies ', like gnats and fish fry and tadpoles, and of 

 terrestrial forms, hke grubs and caterpillars and mice ; 

 there is the correlated impression of the abundance of death, 

 out of a million oyster-embryos but one survives ; there 

 is the plasticity or modifiability of young things, the 

 experimental tricks that can be played with tadpoles, for 

 instance, being notorious. Another impression we get is, 

 that the young creature does often in some measure climb 

 up its own genealogical tree, for there is a great truth in the 

 seductive and much-abused doctrine of recapitulation. 

 Many reservations must be made, e.g. that the hving 

 creature is specific, itself and nothing else from first to 



