ADAPTATIONS TO HAUNTS AND SEASONS 295 



freshwaters of the eastern tropics, are remarkable for the 

 shortening of the abdomen, beyond which the wings, when 

 at rest, extend for a considerable distance. Examples of 

 Metrocoris, found on the surface of estuaries and harbours 

 are often wingless, and these were supposed to belong to a 

 distinct genus (Halobatodes) until F. Meinert (1888) showed 

 that at least some of them must be regarded as ** un- 

 developed forms " — that is abnormally wingless adults — 

 of various kinds of Metrocoris. Such insects suggest 

 therefore the transition towards an entirely wingless con- 

 dition, and this state is characteristic of the remarkable 

 genus Halobates (Fig. 75), whose members, not only marine 

 but usually oceanic in their habitation, are, as might be 

 expected, very greatly modified in form. Of small size — 

 few species attain a length of J in. — they are smoothly 

 ovate (Fig. 75), dark and convex above, paler and flattened 

 beneath, the whole body covered with a dense velvety pile. 

 The moderately strong fore-legs (Fig. 75, c) bear curved 

 claws, set in a cleft of the foot, by which they can anchor to 

 floating objects. Owing to a great backward extension of 

 the middle region of the thorax, the intermediate and hind 

 legs come to be inserted close together (Fig. 75, ^) ; they are 

 very long and slender with rigid thighs and shins. The shin 

 and long first foot- segment (^) of the intermediate leg are pro- 

 vided with a delicate fringe of long hairs, a beautiful adapta- 

 tion for water-surface walking. As the abdomen is markedly 

 shortened, the bases of these long legs seem thrust back 

 to the tail end of the body. The extreme modification of 

 body-form in Halobates is worked through in every genera- 

 tion, for the young (Fig. 75,/) show the normal segmentation 

 of their family and resemble immature Gerris rather closely. 

 Most of the known species are described in the " Chal- 

 lenger " monograph of F. B. White (1882). They range 

 widely over the warmer seas of the globe ; stray examples 

 have been found in the Atlantic as far north as Spain and 

 Carolina. Their habits have been studied by J. J. Walker 

 (1893) ^^^ others. They are most abundant near the 

 shores and have been observed jumping about on seaweed 



