Packard.] INSECTS OF THE POND AND STREAM. 149 
narchys retains its larval tracheal gills, and Dr. Gerstaecker 
has lately discovered that this is also the case with a species 
of Diamphipnoa from Chili, and a European species of Ne- 
moura. This is analogous to certain Tritons or Salamanders 
which retain their gills in adult life. 
The larva of Hydrophilus, the large water beetle (Fig. 
102), breathes by means of spiracles, but is probably aided 
by the lateral filaments along the abdomen. One would 
hardly suspect that the whirligig beetle which gyrates almost 
unceasingly on the surface of every roadside puddle or eddy 
of the stream, had young of such a singular appearance. 
They differ from all known coleopterous larvae in the posses¬ 
sion of eight pairs of large, long, thick, hairy appendages 
permeated by tracheae. They would by 
some be mistaken for caddis worms, but 
their head is much larger and jaws much 
longer and sickle-shaped. In August 
the mature larvae are said to creep out of 
the water and spin an oval cocoon at¬ 
tached to some plant, and then dropping 
their tracheal gills, with their larval 
skins, breathe through spiracles. After 
remaining a month in the pupa state it 
appears as a beetle, which lays its eggs 
in regular rows on the leaves of water plants, and in about 
Gyrinus and larva. 
a week after the larvae are hatched. 
An interesting chapter might be written on the sense of 
sight in aquatic insects. In Notonecta and Corixa the eyes 
pass under the water level, so that they can see above and 
below at the same time. So with Gyrinus (Fig. 113). Its 
eyes are divided by the portion of the head that carries the 
antennae, so that, as Wood says, the portion under the sur¬ 
face may be compared with a water glass used by fishermen 
for observing objects at the bottom. Our Gyrinus larva 
repeats with great exactitude the form of the young Cory- 
21 
