CORKODENTIA AND STONEFLIES. 31 



The tarsi have three joints, the front ones are of very singular 

 form. 



The species are sometimes met with singly, but they are often 

 social in their habits, and have been found ^congregated in a mass of 

 webs, an example of which is exhibited (1311). 



They occur in S. Europe, Asia, Africa and America. 



Sub-Order CORRODENTIA. 



These are small soft-bodied insects with incomplete meta- Table- 

 morphoses. The head is free, generally rather large, wide, with case 35 - 

 prominent eyes. The mouth is provided with mandibles. The 

 antennae are long, composed of about a dozen joints. The prothorax, 

 mesothorax and metathorax are nearly equal ; the prothorax not 

 very large. The wings are four, with a few branching veins which 

 take curious curves ; the hind pair smaller than the front pair. The 

 front pair are held roof -like when at rest ; the hind pair slightly 

 folded at the base. The tarsi have two or three joints. 



Some species never have wings. 



These insects are very common on trunks and branches of trees. 

 Many kinds prefer dead wood. 



One kind, Atropos divinatoria (1316), is very common in houses, 

 especially if damp. It is sometimes destructive to collections of 

 plants or insects. It is one of the insects called Death-watches. 

 It makes a regular tapping noise, probably by striking its jaws 

 against the wood it is resting on, the sound much resembling the 

 ticking of a watch. It can only be heard in a room where there is 

 absence of noise. 



Sub-order PLECOPTERA. 



The Perlidce or Stoneflies (1 320-1 325) are insects of moderate size, 

 with incomplete metamorphoses. The head is slightly imbedded in the 

 prothorax ; with long, slender antennaa composed of very numerous 

 joints. The hind wings are larger than the front ones ; held 

 horizontally over the back when at rest, with the inner portion of 

 the hind pair folded. The tarsi have three joints. The larvae live 

 in water, feeding on decayed vegetable matter, but some are 

 carnivorous. When fully grown they crawl out of the water, the 

 skin splits down the back, and the perfect insect emerges. The 

 adults frequent trees and are very active. 



