NOVKMBER, IDOL] 



KNOWLEDGE. 



2'1.7 



or three niariiie species closely allied to Rliagovelia. 

 have been discovered on the surface of tropical American 

 seas — in all cases close to land, and in consequence of 

 the reniarkalile devclojinicnt of this " wliocl-foof " have 





Fio. 4. 



Img. 3. 



Fio. 5. 



Fig. 3. — Trochopits plumhens (female), Jaiiiaicii. Magnified 9 liiiii's. 

 Fio. 4. — Teriniiial Segment of seoonil loot. Magiiifiiil 75 times. 

 Fio. 5. — Arraugemeut of ciliated Iniri. JIagniiied l.'iC times. 



received the name of Trochopus.|| These bugs (Fig. 3) 

 arc covered with a dense velvety pile which prevents 

 them from being wetted. Occasionally at least they 

 dive beneath the surface of the water, when they carry 

 an air-bubble down with tliem. Another marine wing- 

 less relation of Vclia was discovered ou 'Cartier Island 

 in the Timor Sea by Mr. J. J. Walker, and made by 

 Dr. Bergroth*^ the type of a new genus — Halovelia. 



Of the same general build as Velia. but with narrower 

 body and much longer and more slender legs, the true 

 ■'pond-skaters" — various species of the genus Gerris - 

 may be seen disporting themselves, both in winter and 

 summer, on stagnant and running fresh-waters in our 

 islands. The only insects that venture on a life on the 

 ■■ high seas ai'e near relations of these familiar 

 aquatic Bugs. Of course the oceanic habit has been 

 gained by degrees, and the gradual process of niorlilica- 

 tion can be traced among the related genera. 



The aquatic Bugs of the genus Metrocoris*^ 



lifi't 



from those of Gerris. among other characters, in the 

 much shoi-tcned hind-body beyond which the wings, 

 when at rest, extend for a considerable dist<tnce. Some 

 of the species inhabit fresh-waters in the eastein tropics, 

 while others, in which the wings are absent, are found 

 on the surface of salt-water in estuaries and liafbours. 

 These wingless bugs were classed with the oceanic Halo- 

 bates to be described below, until Dr. Buchanan White 

 referred tlicm to a distinct genus Halobatodes. 

 Recently Dr. Meinert has shown that, in some cases at 

 least, these estuarine insects must be regarded as " un- 

 developed forms" of their winged fiesh-watcr relations. 



il G-. H. Cai-penter. "A new Marine Hydrometrid. " Knt. Mo. 

 Maq. {2)Xo\. IX., 1898, pp. 78-Sl, 109-11 1, pi. III.— G. C. Champion. 

 " Biolofria Central! .imericani." Heuiiptera-Heteroptera. Vol II 

 1898, pp. 140-1, pi. 9.— G. W. Kirkaldv. " .\quatio Hlivnehota."' 

 Bollet. dei Musei di Torino, Vol, XIV., 1899, No. HoO, pp. 4-6. 



•" K. Bergroth. " On two Halophilous Hemiptera." F.iit. Mo. 

 Mag. (2) Vol. IV., 1893, pp. 277-9. 



•* F. Meinert. ' Slaegten Metroeoris og dens ' Forma pragma- 

 tiii-a' Haloliarodes." Entom. Meildelt., Vol T., 18S8, p. 14U. 



We see, therefore, insects iu the very act of adopting 

 a marine life and losing in consequence the power of 

 flight. In several fresh-water Gerrid;e — Vclia nirniix is 

 a not;ible example — both winged and wingless adult 

 forms occur. Apparently an insect, whose fre8h-watc;r 

 homo may occasionally dry up, needs some winged 

 individuals to seek a fresh breeding-place and perpetuate 

 the .species. But those who have ventured on the bosom 

 of a great estuary have what is practically a boundless 

 surface of water over which to glide. Wings, therefore, 

 are not only unnecessary, but as we have seen in the 

 case of the marine flies (p. 198, above) rather a source 

 of danger, which can bo advantageously given up. 



The estuarine Metroeoris, then, with its mixture of 

 winged and wingless species, leads us on to the truly 

 oceanic Ilalobates, in which wings arc altogether un- 

 known. As in marine insects generally, the size of these 

 bugs is small — a body-length of j inch is unusual. They 

 are smooth oval insects, rounded and dark coloured 

 above, flattened and pale below, the body covered with 

 a dense velvety pile that keeps them dry. The fore-legs 

 arc rather stout and adajitcd for seizing floating objects, 

 while the great development and fusion of the two hinder 

 thoracic segments thrusts the long slender middle and 

 hind-legs bat'k to the tail-end of the body, the abdomen 

 being greatly shortened. An especially bcantiful 

 adaptation for their surface-walking is seen in the 

 delicate fringe of long hairs borne on the shin and first 

 foot^segment of the legs of tlic middle pair (Fig. G), 



The earliest discovered sjjecies of Halobates were 

 described by the Russian naturalist Esehschollz in 



l'"io. G. 



Fia. 7. 



FiS. H. 



Fig. 9. 



Fk;. fi. — Halobiile.s re/ialix (male), Torres Strait.-*. MagniGeil 

 4 times. 



Fio. 7. — Underside of abdomen (male). 

 Fia. B. — Underside of abdomen (female). 

 Fig. 9. — Nympli. Magnified 4 times. 



Magnified (i times. 



1822. All the references to these insects made by 

 writers during the succeeding sixty years may be found 

 in Buchanan White's admirable monograph of the genus 



