TRACHEATA 363 
Sub-order 1. Heteroptera. 
CHARACTERISTICS.— Zhe Heteroptera have the proximal half of 
their anterior wings horny, the distal half membranous ; 
they lie flat, overlapping one another. Many are apterous. 
The prothorax is large and free. The proboscis arises from 
the front part of the head, and when at rest lies against the 
thorax. 
A few families may be mentioned : 
Family NoroNECTIDAE (water-boatmen).—These insects 
always swim on their back, which is convex, like the bottom 
of a boat, whilst the ventral surface is flattened. The legs 
are long, especially the posterior pair, which are flattened for 
swimming. They fly well, but can scarcely walk; when dis- 
turbed they dive beneath the surface, carrying a supply of air 
for respiration beneath their wings. They remain for some 
time under water, holding on to aquatic plants, ete. 
Family NEPIDAE (water-scorpions).—The members of this 
family are provided with a pair of long tracheal tubes at the 
end of their abdomen. Their body is flat and oval (Vepa), or 
elongated and linear (Ranatra); their fore limbs are raptorial, 
their hind limbs adapted for swimming. They are carnivorous, 
living chiefly on the larvae of aquatic insects and young fish. 
Their eggs are laid in the water, on stems of plants or under 
stones. 
Family HyproBaTIDAE.—Aquatic insects of oval or elon- 
gated form, which run rapidly on the water’s surface, and are 
usually found in colonies. The antennae are four-jointed and 
unusually long. There are often two adult forms found at 
the same time—one kind being winged, the other wingless. 
This family includes the Halobates, a marine insect found 
swimming on the surface of the sea in the tropics. It feeds 
on dead animals which float on the surface, and is said to 
attach its eggs to the Sargassum sea-weed. 
Family Repuvupar.—A very large and diverse family, 
including many insects of brilliant colour and some of con- 
siderable size. The proboscis is short and three-jointed. They 
are predaceous, and live for the most part on the blood of 
