no ]\Ii-. F. Balfour-Brownc on the 



protected by an elongated, more or less pointed, chitinous 

 " tongue '' (b), which lies forward along the side of" the main 

 lobe and in a groove (//) specially shaped for if. On the 

 outer lace of this ''tongue" is a groove {g), which com- 

 mences sometimes near the apex and sometimes about iialfway 

 back, according to the species, and extends backward beyond 

 the base of the tongue and down the dorsal aspect of the 

 jodeagus to its base (.y'j. 



On the side of this tongue or immediately posterior to it is 

 a curious mass of material ((/), which in several species partly 

 bulges outwards to form a small " wing " (d'). This pale- 

 coloured material is apparently an expansible sac and is 

 easily distinguished from the dark surrounding chitiu. 1 

 imagine that it is in the wall of the ductus, and capable of 

 being bulged outwards, perhaps in the passage of the sperma- 

 tophore (4). The groove already referred to, on the outside of 

 the tongue, passes immediately dor.-al to tiiis saccular region. 



On the right side of the aideagus there is in some species 

 a thin membrane which I have called the " hood " (c). It 

 arises some way behind the apex of the main lobe, and varies 

 considerably in extent. Sometimes it reaches nearly to the 

 base of the aideagns, and stands up merely as a flat mem- 

 branous structure (e. g., //. rxificoUis, heyden'i), and in one 

 case (/i. immacidatus) it folds rigiitover the convexity of the 

 ajdeagus, so as to shut in a considerable portion of the right 

 side of it. In some cases this hood is reduced to a minute 

 lobe (e. g., H. nomax), and in others it is entirely absent. 



I have mentioned that Sharp's figure of the ajdeagus of 

 //. /«/f?<s represents one of the simpler types, and we can 

 trace various stages in complexity in the different species. 

 Tiie simplest types have no " hood " and no " saccular region," 

 e. g., //. apicalis and fluviatdis. H. nomax has the merest 

 trace of a hood, but possesses an elaborate saccular membrane. 

 J], wehnckei has a larger and quite distinct hood and a well- 

 marked saccular membrane. H. rujicollis and heydeni have 

 both structures better developed, and H. immacidatus has a 

 well-marked saccular region and the higiiest development of 

 hood. 



The male armature of Ilaliplus is built upon exactly the 

 same general lines as that of Dytiscus^ whicii has been 

 described by various authors. Berlesd (3, p. 320) calls the 

 main lobe the " hypopliallus" and tiie tongue the " epi- 

 phalius." Blunck (4) speaks of them as the " penis ^' and 

 covering-piece ('' Deckapparat '^), while Sharp (19) calls 

 them " median lube " and " membranous tongue.^' In 

 Ih/liacus, iiowever, the whole armature is fairly symmetrical, 



