NARRATIVE OF THE CRUI8E. 
5X3 
Halobatodes) the only insects with an organisation adapted to a truly pelagic mode of 
life. The head, in addition to the antennae (fig. 179, a), bears three tubercles on either 
side, surmounted by a single hair, but of unknown function. The mandibles are pointed 
and serrated, and serve to puncture the creatures upon which they feed, whilst they suck 
out the juices through a kind of tubular proboscis formed by the united maxillae. The 
thorax forms by far the largest part of the body ; the first segment is transverse and 
collar-like, the second and th ir d elongated and fused, and produced behind and below into 
the acetabula with which the hinder legs are articulated (fig. 179, £ , $ ). The abdomen 
is larger in the male than in the female ; it consists of six ring-like segments followed by 
three others specially modified (fig. 179, g,g.a). The abdomen of the female consists of 
Fig. 179. —Halobates wullerstorffi., Frauenfelcl. 
<5, Male, upper side ; <? , outline of the body of the female ; a, antenna ; ft, front tarsus ; fta, front tarsus of the larva ; 
m.t, middle tibia and tarsus ; g, genital segments of the male, from above ; g.a, the same in profile. 
the same number of segments and carries an ovipositor made up of four valves ; in both 
sexes the ventral surface of the first segment bears a curious tubercle whose extremity is 
pierced by a transverse perforation. The fore-legs are short, and for the greater part of 
their length lie well in advance of the body, without being raptorial they are fitted for 
grasping ; and the second joint of the tarsus is furnished with two curved sharp-pointed 
claws, as well as a thin ribbon-like process (fig. 179 ,ft). The two hinder legs are long, 
and by their means the little creatures scud over the surface of the water. 
The tarsus of the middle legs (fig. 179, m.t) has a fringe of long hairs, which probably 
serves to aid the animal in swimming or to prevent its being so readily driven by the 
wind. 
