86 METAMOBPHOSES OF MAN 



the contrary, there are many of them which never 

 possess any organ of flight at all. Insects which 

 undergo no metamorphoses can never have wings. 

 This is what occurs in all those insects, such as the 

 lice, spring-tails, and lepismse, which leave the egg 

 fully formed, and only increase in size afterwards. 

 These are purely oviparous animals, and their develop- 

 ment is effected by a series of simple transformations; 

 they never reach the condition of the perfect insect, 

 and as regards external characters, they remain larvae 

 to the end of their lives. 



continents, and engender plague or typhus by the putrefaction of 

 their bodies, after they have produced famine by their voracity. 

 Although these large orthoptera measure nearly ten centimetres 

 om wing to wing, single individuals cannot undertake long jour- 

 neys. The flight of an isolated insect is heavy, and moreover is 

 never sustained for any length of time. It is in great part the wind 

 which drives these living clouds to such immense distances, occa- 

 sionally carrying them out to sea. 



