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ENTOMOLOGY 



though commonly restricted to the sides of the abdomen, where they 

 occur in pairs or in paired clusters (Fig. 20, A). Caudal gills are found 

 in agrionid nymphs (Fig. 173). The aquatic caterpillars oiParaponyx 

 (Fig. 174) are unique among Lepidoptera in having gills, which are 

 filamentous in this instance. 



Caddis worms, enclosed in their cases, maintain a current of water by 

 means of undulatory movements of the body, and the larvae and pupae 

 of most black-flies (Simuliidae, Fig. 233) secure a continuous supply of 

 fresh air simply by fastening themselves to rocks in swiftly flowing 

 streams. 



Rectal respiration is highly developed in dragon fly nymphs. In 

 these, the rectum is lined with thousands of 

 tracheal branches, which are bathed by water 

 drawn in from behind, and then expelled. 



All these kinds of respiration cutaneous, 

 branchial and rectal occur in young ephemerid 

 nymphs; while mosquito larvae have in addition 

 spiracular respiration. 



With the arrival of imaginal life, tracheal 

 gills disappear, except in Perlidae, and even in 

 these insects the gills are of little, if any, use. 



Marine Insects. Except along the shore, 

 the sea is almost devoid of insect life, the excep- 

 tions being a few chironomid larvae which have 

 been dredged in deep water, and fifteen species 

 of Halobates (belonging to the same family as 



our familiar pond-skaters), which are found on warm smooth seas, 

 where they subsist on floating animal remains. 



Between tide-marks may be found various beetles and collembolans, 

 which feed upon organic debris; as the tide rises, the former retreat, 

 but the latter commonly burrow in the sand or under stones and become 

 submerged, for example the common Anurida maritima. 



Insect Drift. Seaweed or other refuse cast upon the shore harbors 

 a great variety of insects, especially dipterous larvae, staphylinid scaven- 

 gers and predaceous Carabidae. On the shores of inland ponds and 

 lakes a similar assemblage of insects may be found feeding for the most 

 part on the remains of plants or animals, or else on one another. During 

 a strong wind, the leeward shore of a lake is an excellent collecting 

 ground, as many insects are driven against it. On the shores of the 

 Great Lakes insects are occasionally cast up in immense numbers, form- 



A B 



FIG. 233. Simulium;. 

 A, larva; B, pupa, show- 

 ing respiratory filaments. 



