Marvels of the Universe 727 
suggests comparison with the outriggers on racing skiffs. 
The rowing of Gerris is effected by the middle pair of legs, 
which are much longer than the others. The purpose of 
what looks like their purposeless movements on the water 
is to keep a sharp look out for the larve of other aquatic 
insects, which are secured by the front pair of legs until the 
sharp beak can be inserted like a dagger and the victim’s 
blood sucked. 
More remarkable than Gerris in appearance is Hydro- 
metra. Only half an inch long, its length is twelve times its 
greatest breadth. Its head is drawn out to such an extent 
that it accounts for two-fifths of its entire length, and the 
eyes are situated half-way along the head. Its general 
appearance is much like a miniature copy of a Stick Insect, 
to which, however, it is in no way related. In this species 
the wings are undeveloped, only the merest rudiments of 
them being discoverable. The legs, though of considerable 
length, are reduced to the minimum of thickness ; but they 
are used for walking instead of rowing. These insects are 
so extremely slender that they require to be looked for very 
closely. 
The Water Cricket of the angler is not a cricket at all, 
but one of these Water Bugs known to entomologists as 
Velia. It is built more on the lines of Gerris than of 
Hydrometra, and it is very like Gerris in its movements. 
It may be distinguished from the latter by its greater 
breadth, its broadest part being between the bases of the 
wings and forming the middle line of a diamond-shaped 
area including the head and a space between the folded 
wings. I should say, if the wings are there to be folded, 
for it is only occasionally that the wings are developed. It 
appears as though a small percentage of individuals are set 
apart by Nature to be explorers, and provided with wings 
that they may leave the piece of water where they were 
born and seek unoccupied ponds for the purpose of popu- 
lating them. When the wings are present they are dark- 
brown with several white spots; in their absence the 
insect may be known by the presence of two orange ridges 
along the back. Somewhat similar related forms to Velia 
are Microvelia and Mesovelia, which must be looked for 
among the water-weeds and bog-moss ; but they are only 
about a fourth of the size of Velia, and so must be searched 
for very closely. 
No such difficulty, however, attends the detection of 
Ranatra, if it is present in the pond you are investigating, 
for it exceeds two inches in length, from the tip of the short 
beak (which is always kept extended), to the end of the tail 
bristles—which, however, account for a third of its length. 
But its apparent length is considerably increased by the 
Photo bu| [H. Main, FPS. 
“WATER CRICKET.” 
An adult that has not developed wings. 
Photo bu) [H. Main, ES. 
HYDROMETRA. 
This Water Bug might be taken for a 
newly hatched Stick Insect. 
