FIELD BOOK OF INSECTS. 



2. Hind legs not more than twice as long as the front 



3' 



Hind le^s more than twice as long as the front; ab- 

 dominal constrictions slight. Cylindrical case of sand and 



. . LEPTOCERID.E. 



small stones . 



3 Head longitudinally elliptic, at slight angle with the 

 body only head and pronotum chitinized; abdominal 

 constrictions deep; hind legs slightly longer than the front. 

 Case of vegetable matter laid longitudinally and forming 

 a spiral, widening at the anterior end PHRYGANEID*. 



Head oval to round; usually more of the thorax 

 the pronotum chitinized ; abdominal constrictions slight . . 4. 



Lateral fringe well developed. Cases various 



LlMXOPHILID^E. 



Lateral fringe slightly developed. Case of sand or 



SERICOSTOMATID^S. 



small stones 



e Abdomen much thicker than the thorax, 

 kidney-shaped, of small stones; or flat and parchment- 



. HYDROPTILID/Z. 



like ( 



Abdomen little, if any, thicker than thorax 0. 



6 Hind legs about the same length as the front ones. 



No portable larval case. HYDROPSYCHID^. 



Hind legs a little longer than the front ones. 



RHYACOPHILID^E. 



larval cases 



The ancestral tree of insects is buried to 

 TheAnces- beyond the origin of the branches in the 

 tral Tree oblivion of the past. We have been look- 



ing at the lower part of certain branches and on one 

 of them we got rather close to the roots when we were 

 examining "the most primitive insects." Partly 

 convenience, but also because the branches are so tanglec 

 and their points of union are so hidden, we have not kept 

 to a single branch. When we were at the Trichoptera, 

 we were near the point where one of them blossoms out 

 into Lepidoptera. It is believed that incomplete meta- 

 morphosis is one of the signs of primitiveness and we will 

 now go down near the trunk again but in another part 

 the tree. Rather than start with forms not usually noticec 

 by any but professionals, we will begin with earwigs: 



60 



