110 THE ENTOMOLOGIST. 



up all the water within that area, would cause all the species 

 represented in that year by apterous individuals only to become 

 extinct. Such cases will be familiar to those who have studied 

 the aquatic Ehynchota-fauna of any locality for a consecutive 

 number of years. Where, however, there are a few macropterous 

 individuals, these will be able to emigrate to " pastures new " to 

 found a fresh colony, which in course of time may, or may not, 

 repeople the original habitat. 



In confirmation of this, it may be noted that the occurrence 

 in comparatively large numbers, or the apparently complete dis- 

 appearance, of the macropterous individuals, does not seem to 

 have any connection with the dryness or wetness of any particular 

 year or years. 



Aepophilus bonnairii is, as one would expect, always (so far as 

 yet known) brachypterous, practically apterous. Its habitat 

 never dries up and its range along the sea- shore is to all intents 

 limitless ; thus migration is unnecessary, and the organs of 

 flight have become reduced to their present vestigial condition. 



Migration usually takes place during the night, and waterbugs 

 (like other aquatic insects) are often misled by the reflection of 

 the moon to mistake the glass roofs of conservatories and other 

 similar buildings for the surface of still water. Electric light, 

 or indeed any very strong light, proves a great attraction, causing 

 (particularly at its first installation) a migration of certain water 

 insects from outlying habitats to ponds near the light. This 

 was especially remarked — owing chiefly to the great size of the 

 objects — some years ago in Washington (U.S.A.), where speci- 

 mens of the Giant Waterbugs (Belostoma and Benacus) were often 

 found lying on the pavements of the city in the early morning.* 



Mr. Malcolm Burr, while travelling last summer in Hungary, 

 captured and forwarded to me a specimen of Gerris thoracicus, 

 Schumm., which had alighted upon the dinner table, and Mr. 

 E. E. Green has given me an example of a new bug (Gerris 

 tristan, Kirk.) taken under similar circumstances in Ceylon. 



Mesovelia Mulsant & Bey, + is another genus of uncertain 

 position, having been referred indifferently to the Hebridse and 

 to the Gerridas. One species, M. furcata, M. E., is British and 

 is usually apterous, being then a slender thin-legged green crea- 

 ture, readily distinguished — with Ilebrus — from the other semi- 

 aquatic genera by the possession of two ocelli. The coxa3 are 

 practically contiguous, and the mesonotum is not concealed by 

 the pronotum. The thoracic structure in the winged forms is 



* ' Proc. Ent. Soc. Wash.' iii. pp. 87-8. See also Fletcher, 1884, in 

 ' Entoni.' xvii. p. 21. 



| fjnaoq i^mcsos) middle, and " velia" ; of the latter I do not know the 

 derivation — possibly from French velours (velvet), in allusion to the pubescent 

 under- surface of the body ; or, more probably, from the Latin velum, a sail : 

 e.g., vela dare, to set sail, as an appropriate name for a waterbug. 



