REPORT ON THE PELAGIC HEMIPTERA. 75 



may be part of the meclianism employed.^ Observations are however very desirable on 

 these points. 



The absence of elytra and wings seems to be constant in Halohates, and on this 

 account some authors formerly thought that the known specimens had not reached the 

 adult condition. M. Fairmaire's discovery of eggs proved that this theory was erroneous, 

 but an examination of the genital segments would have shown tlie same. The absence of 

 wings and elytra is not unfrequent in many species of allied genera which live on the sur- 

 face of fresh water ; '" and in their case the advantage, to the species, of the possession of 

 these organs is intelligible, especially when they inhabit, as is often the case, small pools 

 or marshes liable to be dried up in summer, or capable of supporting a limited number 

 only of individuals. But to species which dwell on a practically inexhaustible surface as 

 the sea the possession of wings would seem unnecessary, if not positively a disadvantage, as 

 making their possessors and users liable to be carried off l)y the winil, and, if not blown 

 to some inhospitable spot, separated at least from their companions, a probable disadvan- 

 tage to gregarious species as the Halohates are. 



Unless it has been derived from a fresh-water progenitor, — which is of course 

 possible, but in view of its structure perhaps not very probable, —it seems likely that 

 Halohates has never possessed wings. On the whole, there are good grounds for thinking 

 that Halohates, if not the actual ancestor of its fresh-water allies, is much less differen- 

 tiated from the common ancestor than they are. The small or apparently rudimentary 

 condition of the abdomen which gives the adult Halohates so strong a resemblance to 

 the immature Gerris, must not l)e lost sight of in this connection. 



Amongst many points which rec[uire investigation in the life history, especial attention 

 should be directed to the following : — 



1. The food, and the manner in which it is seized and retained. 



2. The manner of locomotion, and especially whether all the species have the 



power of diving beneath the water. Experiments may also be made as to 

 the effect of compulsory submersion. As several writers have mentioned 

 that specimens obtained by the tow-net have always been dead, it is 

 probable that submersion means, in some cases, death by drowning. 



?,. What enemies they have; if they are eaten by any other animals; and what 

 means of defence they have. 



4. The use of the several peculiar organs or f^tructures, such as the ocelli-like 

 tubercles of the head ; the perforated tubercle at the base of the ventral surface 

 of the abdomen ; the ribbon-like process connected with the claws of the tarsi, 



1 Thou-k I am not yet .iiiite certain, I think that in the species wliose usual hicality is the open sea tlielong frinj;e 

 is longer than in those which dwell near the shore. The material at hand is not sulhcieiit to clear up this point. If it 

 be the case, the reason for it seems obvious. 



= It is to be noted that this aljsence of wings is not necessarily .lue to an afpiatic- lifr, for mosl, if nut all, of the 

 Hydrocorisa have well-developeil wings, which they not unfrequently use for aerial (light. 



