Ill AQUATIC HYMENOPTERA 221 



Both species are fond of creeping along the sides of 

 the vessel in which they are kept, or on the leaves 

 and stems of aquatic plants ; but very frequently they 

 quit their support and swim boldly out into the open 

 water. As the motion in Polynema natans is caused 

 by the wings, it might almost be called a flight ; owing 

 however to the density of the medium and partly to 

 the direction in which the wings act, the movement, 

 though not inelegant, is slow, and is rather a succes- 

 sion of jerks than a continuous progression. ... I 

 was unfortunately unable to ascertain whether they 

 could fly ; taking my opportunity when they were 

 out of the water, I teased several specirhens of Poly- 

 nema 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 com- 

 petition. 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. 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 arc admirably adapted to 



