NATURAL HISTORY STUDIES 



The Great Change 



Within the cocoon the body of the larva is broken 

 down and is built up again on a new architectural 

 plan. Clusters of active cells become the centres 

 of new formation, and wandering cells, working 

 like sappers and miners, transport material from 

 place to place. Although the breaking-down which 

 precedes the reconstruction is never so thorough- 

 going as in flies, where the pupa returns almost to 

 an egg-like state, there is a gradual change of 

 almost all the organs. One may compare what 

 occurs to a not unfamiliar sight, the piecemeal 

 pulling down of a large building, such as a railway 

 station, and its piecemeal rebuilding, all so arranged 

 that the activity and what is life but activity ? 

 does not come to a standstill. 



When the reconstruction is completed which 

 may take a couple of weeks or as many years the 

 fully formed insect emerges from the pupa -case 

 its last moult. It is often rather soft and flabby 

 on its emergence, but it soon hardens up and there 

 is no more growing. Many of the details of the 

 liberation of the butterfly or moth are extremely 

 interesting, thus there are often lids which open 

 neatly ; there is sometimes a special " case opener " 

 that helps the escape, just like the " egg -tooth " 

 with which young birds break through the egg-shell ; 

 the puss -moth secretes caustic potash from its 

 mouth which dissolves away the pupa-case. 



30 



