THE LIFE CYCLE 



345 



one to the other is incompatible with the ordinary use of 

 the organs, the quiescent pupal stage comes in as a transi- 

 tion stage, a period of making over, during which the neces- 

 sary extensive alterations of the body are effected The 







FIG. 197, The larva of 

 undulatus). 



a diving beetle (Hydroporus 



pupal stage is peculiar to insects, and its presence or 

 absence within the group distinguishes between the so-called 

 ' 'complete" and "incomplete" metamorphosis. 



PIG. 198. The pupa of the 

 same diving beetle (drawn 

 by Miss Helen V. William- 

 son). 



FIG. 199. The adult diving 

 beetle (Hydroporus undu- 

 latus). 



