126 



BRANCH ARTHROPODA 



are beneficial, our crops will be the larger and more profitable, 

 and our bodies more secure from disease. 



Classification, — Entomologists vary in their opinions as to 

 the number of orders into which the Class Insecta should be 

 divided. Packard's "Guide" (1883) gives eight orders, while 

 Comstock's "Manual" (1895) and Kellogg's "American Insects" 

 (1905) each give nineteen orders. Kellogg says, " In the first 

 place the author believes that this classification^ best represents 

 our present knowledge of insect taxonomy; in the second place, 



if 



Fig. 97.— Adult silkworm: 1, Head; 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, rings; 

 11, horn; 13, three pairs of articulated legs; 14, four pairs of abdominal 

 or false legs; 15, a pair of false legs on the last ring. (Farmers' Bull. 

 165, U. S. Dcpt. of Agriculture.) I'he silk glands of caterpillars are ho- 

 mologous with the true salivary glands of other insects. — Folsom. 



this is the classification taught by nearly all the teachers of 

 entomology in America." 



Students wishing to study insects in detail should consult 

 either Comstock's or Kellogg's large work on insects. 



ORDER I. AP'TERA OR THYSANU'RA 

 These are small or minute wingless insects which undergo 

 no metamorphosis. The body is covered with hairs or scales. 

 There are several pairs of rudimentary abdominal appendages, 

 probaV^ly vestiges of abdominal legs in ancestors. The mouth 

 parts are adapted for biting. " Their internal systems of organs 

 have a segmental character corresponding to the external seg- 

 mentation of the body."2 They live in sugar boxes and pan- 



Comstock's classification. 



Kellogg, p. 59. 



