Packard] IXSECTS OF THE PO?^D AND STREAM. 149 



Fig. 113. 



narcbj's retains its larval tracheal gills, and Dr. Gerstaecker 

 has lately (liscovered that this is also the case with a species 

 of Dianiphipnoa 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 Ilydrophilus, 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 everj^ roadside puddle or eddy 

 of the stream, had 3'oung of such a singular appearance. 

 They differ from all known coleopterous larvae in the posses- 

 sion of eight pairs of large, long, thick, hair}^ 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, witli their larval 

 skins, l)reathe through si)iraclcs. After 

 remaining a month in the })upa state it 

 appears as a beetle, which lays its eggs 

 in regular rows on the leaves of water plants, and in about 

 a week after tlie larvre 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 



Gyrinus and larva. 



