354 NATURAL ARRANGEMENT OF INSECTS. 



enable them to make their burrows. They possess 

 three long legs attached to their large thorax, all of 

 which are bent forwards : their branchiae are affixed on 

 each side of the abdomen ; and of these there are usually 

 seven pairs, which occupy the place subsequently held 

 by the stigmata in the perfect insect ; there are varieties 

 of structure in these organs in the several genera of 

 which the sub-family is composed. Swammerdam in- 

 forms us that they are three years in acquiring their full 

 growth ; this is a remarkable circumstance, considering 

 the shortness of their lives afterwards. Having grown 

 to maturity, in which state anglers make use of them 

 as a bait, they quit their burrows, swim to the surface, 

 where their enveloping case splits, and from which the 

 insect extracts itself with expanded wings, and flying 

 to some neighbouring object on the shore, again uncases 

 itself; for, although it has already acquired its wings, 

 and the power of flight, a delicate membrane still clothes 

 it, of which, however, it speedily divests itself. The 

 insects sometimes abound in such profusion, that the 

 air is completely filled with them, and their dead bodies 

 have been strewed over the land as a rich manure; for 

 their life terminates with the execution of the function 

 for which they were solely transformed, that of 

 perpetuating the species, which is almost instantly 

 accomplished. The chief genera are Oxycypha y with 

 only two wings ; Cloe, with four, but the posterior ex- 

 tremely minute. Bactis and Ephemera have the in- 

 ferior wings larger ; but the former have three ocelli, 

 and the latter but two. 



(312.) Our second sub-family, the Phryganin(z, is 

 of much larger extent than the preceding, and they 

 are known as " May flies." They constitute the order 

 Trichoptera of Kirby. Of all insects, they approach 

 the closest in resemblance to the Lepidoptera, their 

 wings being covered with hairs, or narrow scales ; and 

 in their transformations, also, they have a considerable 

 resemblance to that order ; from which, however, they 

 are sufficiently distinct in having a mandibulated mouth. 



