320 THE RECAPITULATION THEORY 



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 cater- 

 pillar is already an unmistakable 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, and 

 in mode of life, and very usually in mode of nutri- 

 tion. 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 parts of the caterpillar to the 

 sucking proboscis of a moth would inevitably lead 

 to starvation. The difficulty is evaded by retaining 

 the external form and habits of one particular stage 

 for an unduly long period, so that the relations 

 of the animal to the surrounding environment 

 remain unchanged, while internally preparations 

 for the later stages are in progress. Cinderella 

 and the princess are equally possible entities, each 

 being well adapted to her environment. The exi- 

 gences of the situation do not permit however of 

 a gradual change from one to the other : the trans- 

 formation, at least as regards external appearance, 

 must be abrupt. 



