MR. LUBBOCK ON TWO AQUATIC HYMENOPTERA. 137 
of air would quite destroy its equilibrium when under water, and a drop of water would 
equally prevent free motion in the air. The difficulty is, however, mitigated by the fact 
that the air in the trachez requires changing only at considerable intervals. A common 
house-fly placed under water ceased to move in half an hour. My specimens, however, of 
Polynema natans lived under water several hours without suffering any apparent incon- 
venience. One, which I put in a bottle full of water at 7 o'clock in the morning, was 
quite lively at 7 o'clock in the evening, after having therefore been no less than twelve 
hours at least under water. I say at least, because I had no means of knowing how long 
it had been there before my experiment began. Probably, however, this was about the 
limit of its endurance; for four other specimens which I treated in the same manner at 
about 6 o'clock in the evening were apparently dead at the same hour on the following 
morning, and the individual above mentioned was itself motionless at 9 o'clock, or after 
fourteen hours of submersion. Ithen, however, put it in a dry bottle, and next morning 
it was as lively as ever. Wishing to see whether it retained any unpleasant recollections 
of its drowning, I gave it the opportunity of again entering the water, which it imme- 
diately proceeded to do. 
l was unfortunately unable to ascertain whether they could fly: taking my oppor- 
tunity when they were out of the water, I teased several specimens of P. natans with 
the point of a needle, but never succeeded in making one take to its wings, at least not 
in air. When walking on the water, however, they sometimes started off suddenly, but 
always kept close to the surface, so that it rather seemed as if they were carried by some 
tiny gust of air. 
We might almost wonder how an animal like this, with no apparent weapons of 
defence, and no great powers of speed, could maintain itself in this world of competition. 
Protected, however, in its early stages by the victim which it is destroying, it is exposed 
to its enemies but for a short period of its life; and if, like many of its allies, the eggs 
of other insects are the prey which it seeks, speed may be of comparatively little 
importance. : i 
However this may be, we find in the two insects now under consideration no pecu- 
liarities indicative of an aquatic life. Many water-insects are more or less boat-shaped, 
and, both in form and position, the legs are admirably adapted to serve as oars; others, 
again, use the hinder part of the body as a fish does its tail. Here we find no such 
arrangements. In both cases the head is broad; in Prestwichia the hind legs have, 
indeed, some scattered hairs, but not more so than its terrestrial allies ROPA Polynema 
do the wings appear in any way modified to adapt them to their new function. 
Emerson somewhere says, that the population of the world is “not the best, but the 
best that could live now.” Mr. Emerson is no naturalist, or he would surely know that 
the population of the world at any given time is not the best that can live, but the € 
since it is not the best and strongest, but the worst and weakest which, in the diet 6 
for existence, habitually go to the wall. Thus our two amphibious Hy — grs 
though not so fleet or well armed as they might be, not so long able to respire under 
water as some other insects, still maintain their existence, because their enemies are 
unable to destroy them, and they have the field to themselves. 
