Collembola 165 



as to the relations between the orders, which will be 

 discussed in the concluding chapter. 



The pages immediately following are devoted to a 

 short survey of the leading features of the various 

 orders, and of the principal families into which they 

 have been divided. This survey is, of necessity, 

 very brief and incomplete, those characters being 

 specially dwelt upon which serve to distinguish the 

 various groups from each other. It is hoped that 

 enough guidance is given to enable the student to 

 trace an unknown insect to its correct family, and 

 that the references to special literature will then help 

 him to detailed information. The interesting subject 

 of habit is very briefly mentioned in this summary of 

 the orders and families, being dealt with in relation 

 to insects as a whole in the next chapter — that on 

 " Insects and their Surroundings." 



ORDER I.— COLLEMBOLA. 



Structure. — The Springtails, which are com- 

 prised in this order, are wingless insects of small size, 

 usually without air-tubes. The feelers have few 

 segments (4-6) and the jaws pushed back into the head- 

 capsule (flg. 91 ^). A variable number of simple eyes, 

 from one up to eight may be present on either side of 

 the head ; but many springtails are quite blind. In 

 front of the eyes and behind the feelers an oblique 

 groove or rounded depression is often present wherein 

 are situated a number of tubercles forming a " post- 

 antennal " organ of unknown sensory function (fig. 

 91 /'). The prothorax is the smallest of the three 

 segments of the fore-body. The legs have no tarsal 

 segments, a large upper and (sometimes) a narrow 

 lower claw being inserted at the end of the shin (fig. 



