ADAPTATIONS TO HAUNTS AND SEASONS 287 



transfers the insect directly from air into sea-water, one 

 notices that each of its hairs holds a little layer of the surface- 

 film, forming at first tiny spheroids ; these soon unite into a 

 little globule which surrounds its body on every side, and 

 which, despite the agitation resulting from the insect 

 running under the water, never escapes." The air- tube 

 system of Aepus is furnished with two broadly ovate 

 reservoirs in close connection with the hindmost pair of 

 spiracles. These, as Miall remarks, " are no doubt useful 

 during prolonged submersion." The compound eyes of 

 Aepus are remarkable, the corneal facets being circular in 

 form and few in number and protected by a chitinous plate 

 perforated by a central round hole. Adults and grubs of 

 Aepus are believed to prey on small molluscs such as Rissoa, 

 in whose company they may often be seen. 



The most conspicuous of all the sea-shore insects are 

 certainly the Diptera or two- winged flies. Over the mass 

 of seaweed thrown up by the waves at high- water mark run 

 hundreds of small brownish or greyish flies — many of them 

 related to the group of the house-fly and bluebottle. Their 

 maggots feed on the decaying marine vegetation below. 

 The maggot of Fucomyia frigida, described by E. V. Elwes 

 (1915), has the tail-spiracles surrounded by delicately 

 branched bristles, well adapted for holding air-bubbles. 

 Though belonging to several distinct genera — Fucellia, 

 Coelopa, Orygma, for example — most of the seashore flies 

 have a characteristic general aspect which suggests adapta- 

 tion to their strange haunts, a flattened form of body, 

 angular head with small eyes, markedly spiny or hairy legs, 

 and narrow wings. They run rapidly over the dark accumu- 

 lation of wrack, frequently rising and flying for short 

 distances ; their wings are not suited for prolonged flights. 

 On the shores of the windswept sub-antarctic island of 

 Kerguelen live flies of this group described by E. A. Eaton 

 (1879) in which the reduction of the wings is carried still 

 further ; Anomalopteryx marittma, with narrow strap-like 

 wings, lives on the nests of seabirds, while Apetefitts litoralis 

 creeps over the stones of the beach. A. R. Wallace (1889) 



