RELATION TO ANIMAL KINGDOM 17 



usually called a "nymph" rather than a larva, when 

 this has become ripe, it develops wing pads or rudimen- 

 tary wings ; but continues its feeding as in the preceding 

 stages until the period when it moults for the last time 

 and changes to the adult or fourth stage. It thus 

 develops continuously, without conspicuous change of 

 form, and the metamorphosis is incomplete. Our 

 caterpillar, however, after moulting as often as needed 

 to obtain full size, changes into a 

 nondescript creature bearing no close 

 resemblance to its former nor to its 

 future stage and remains in this 

 "pupal" or "chrysaHs" form while 'fk-,.3. -Sect, on through 

 the caterpillar structures are disin- insect crust showing lay- 



ers of chitin at c, the cel- 



tegrated and re-tormed mto butter- luiar layer at h, and the 

 fly parts. This is a complete trans- basal membrane at ;,. 

 formation, in which almost no part 

 of the larval structure remains unchanged, and even 

 the method of feeding may become completely reversed: 

 indeed, in some cases the adults never feed at all, 

 depending entirely upon the supply stored by the larva 

 to mature the reproductive cells or eggs. 



Among themselves insects differ as much in appear- 

 ance and habits as they do from their more remote 

 relations. They are found wherever life is capable of 

 existing at all, and there is no organic substance known 

 which, in one stage or another, is not food for some 

 insect. They are moderately numerous, some 200,000 

 different kinds being already known and described, 

 with the reasonable certainty that we have not yet 

 discovered much more than one-half of those that exist. 



There are some that never become winged; that are 

 soft-bodied in all stages, live usually in damp places 

 and are simply organized: these are the Thysanura, in 

 ^J which the mouth structure is not well developed. 



