THE INSECT WORLD. 55 



With fore-wings thickened at base, thin at the tip ; mouth parts form- 

 ing a jointed beak ; trtmsformations incomplete . . Hemiptera. 



With the fore-wings uniform in texture ; mouth parts and transforma- 

 tions as before Homoptera. 



The fore-wings are liorny, and useless for flight, serving only as a cov- 

 ering for the posterior pair ; mouth mandibulate ; metamorphosis 

 complete Coleoptera. 



All the wings and the body covered with scales ; mouth parts developed 

 into a long coiled tongue ; transformations complete Lepidoptera. 



The wings transparent, with only a few longitudinal veins ; mouth 

 mandibulate, the tongue formed for lapping ; transformations com- 

 plete Hvmenoptera. 



Two wings only ; mouth parts haustellate ; transformations complete 



Diptera. 



CHAPTER II. 



THE THYSANURA. 



Spring-tails, Bristle-tails, Fish-moths, etc. 



Under this term are grouped a number of lowly insects which 

 never become winged, and can hardly be said to have any real 

 transformations. Most of them are small, soft bodied, with 

 feebly developed mouth parts, and live in damp earth, among 

 decaying vegetable matter. Some live under bark of dead or 

 decaying trees, or in decaying wood, while in rare instances spe- 

 cies are found preferring dry and warm localities. Among those 

 that live in damp places are forms without eyes, and wifh no de- 

 veloped tracheal system, the necessary oxygen being absorbed 

 through the skin itself Compound eyes are developed in a few 

 instances only, though ocelli are usually present. 



Peculiar to the order are certain abdominal appendages. In 

 some cases these are in the form of rudimentary abdominal legs, 

 indicating a relationship to the Myriapods or Centipedes ; but 

 more often they consist of bristles or filaments attached to the 

 anal segment. In the simplest form they consist of long, many- 

 jointed appendages, whose function may be tactile, similar to 

 that of the antennae. 



A good example of this type is the little creature known to 



