228 ANIMAL PEDIGREES 



to the other is not a gradual but an abrupt one, at 

 any rate so far as external characters are concerned. 

 Sudden changes of this kind, as from the free 

 swimming Pluteus to the creeping Echinus, or from 

 the sluggish leaf-eating caterpillar to the dainty 

 butterfly, cannot possibly be recapitulatory, for 

 even if small jumps are permissible in nature, there 

 is no room for bounds forward of this magnitude. 

 Cases of abrupt metamorphosis may always be 

 viewed as due to secondary modifications, and 

 rarely if ever have any significance beyond the 

 particular group of animals concerned. For 

 example, a Pluteus larva may be recognised as 

 belonging to the group of Echinoidea before the 

 adult urchin has commenced to be formed within it, 

 and the Lepidopteran caterpillar is already an un- 

 mistakable insect. Hence, for the explanation of 

 the metamorphoses in these cases it is useless to 

 look outside the groups of Echinoidea and Insecta 

 respectively. 



Abrupt metamorphosis is always associated with 

 great change in external form and appearance, in 

 manner of life, and very usually in mode of 

 nutrition. A gradual transition in such cases is 

 inadmissible, because in the intermediate stages the 

 animal would be adapted to neither the larval nor 

 the adult condition ; a gradual conversion of the 

 biting mouth of the caterpillar to the sucking 

 proboscis of a moth would inevitably lead to 

 starvation. This difficulty is evaded by retaining 

 the external form and habits of one particular stage 

 for an unduly long period, so that the relations of 



