78 ANIMAL INDIVIDUALITY [CH. 



of which they are composed, not the living organs 

 themselves, which the animal uses for its further 

 development. 



There is a wide possibility of change inherent in 

 all living substance, but after a certain specialization 

 of cell or organ is reached, it becomes impossible to 

 remodel it to perform another totally different func- 

 tion. I say impossible : it would perhaps be safer to 

 say that the difficulty of remodelling becomes so great 

 that the simplest way, and so the least wasteful of 

 energy for the organism, is to destroy the old structure, 

 degrading it to the level of mere food-material, and 

 then to build up the new from its very beginnings. 



An extraordinary example of this is found in the 

 development of the higher insects. Practically every 

 organ of the body in a larval form like the caterpillar 

 becomes broken down, chiefly by the action of 

 phagocytes, into lumps and masses of dead proteid 

 substances. 



A boy known by repute to the writer once 

 expressed surprise that there were any organs inside 

 caterpillars : " I thought," said he, " that they were all 

 just skin and squash." This would be a very accurate 

 description of their condition during the metamor- 

 phosis, were it not that embedded in the squash at 

 intervals there lie little patches of living tissue. 

 These so-called imagined discs are formed of un- 

 specialized cells ; they grow, unite with each other, 



