372 



SOME REPRESENTATIVE INSECTS 



Arthropoda should be divided. The seventeen that follow repre- 

 sent one of the widely recognized classifications. Such a grouping 

 is not absolute, however, since it expresses only the opinion of 

 some investigators as to what differences are sufficient to justify 



a separation of types. Certain stu- 

 dents of the Insecta think otherwise, 

 and hence may place in a single order 

 some of the types that are here sepa- 

 rated. Others recognize even a 

 greater number of orders. As the list 

 of orders is a long one, we may use a 

 more formal arrangement than would 

 otherwise be chosen. It will be 

 noted that the character of the wings 

 is the feature most commonly used in 

 the names of the orders. 



Orders of the Class Insecta 



Order 1 , Thysanura. — These may 

 be regarded as the simplest of exist- 

 ing insects, because of the absence 

 of wings in embryo and adult to- 

 gether with other primitive features. 

 Common examples are the household 

 pests known as " fish-moths " or 

 " silverfish," Lepisma (Fig. 190 A). 

 ]\Iouth parts mandibulate. Develop- 

 ment direct. Species 175. 



Order 2, CoUemboIa. — These are 



sometimes united with the Thysanura 



in a single order, the Aptera, since 



they are likewise wingless. They are 



known as '' springtails " because of a 



tail-like projection on the ventral side 



of the abdomen by means of which 



they can spring into the air. A 



common representative is the "snow 



^ea," Achorutes nivicola (cf. Fig. 190 B), which appears on the snow 



in spring and is sometimes a pest to the maple-sugar makers. 



Mouth parts mandibulate. Development direct. Species 700. 



Fig. 190. — Wingless insects. 



A, a silverfish, Lepisma saccha- 

 rina, one of the Order Thysanura. 

 B, Achorutes armatum, one of the 

 Order Collembola. (4, from Farmers' 

 Bulletin, No. 681; B, from same, 

 No. 789, U. S. Dept. Agr.) 



