36 NATURAL HISTORY OF AQUATIC INSECTS CH. | 



under side of the wing-covers against the end of the 

 body, and is probably a call to other Beetles of the 

 same species. Gyrinus always makes this sound 

 before taking flight. A flying Gyrinus hums like a 

 Bee, apparently in consequence of the whistling of 

 the air about its hollow wing-covers. 



The female Beetle lays a number of elongate oval 

 eggs, end to end, upon the leaves of water-plants. 

 They are found beneath the surface of the water, and 

 sometimes at a considerable depth. 



Schiodte^ has given an excellent set of figures of 

 the larva of Gyrinus. It is 14 mm. (4 in.) long. 

 Behind the head come three thoracic segments, of 

 which the foremost is protected by a dorsal plate, as 

 is usually the case with burrowing larvae. The legs 

 are long and slender. Each of the eight foremost 

 abdominal segments carries a pair of gills, and the 

 ninth two pairs. A small tenth abdominal segment 

 is armed with two pairs of long, sharp, curved hooks, 

 which are believed to be of use in climbing. The 

 general appearance of the larva is that of a small 

 Centipede. The mouth-parts are those of a carni- 

 vorous larva, the mandibles especially being pointed, 

 perforated by a slit beneath the apex, and suctorial. 

 The gills are long, tapering, and fringed with fine 

 hairs. A tracheal tube traverses each, and gives off 

 many fine branches to the delicate walls. 



It is generally thought to be easy to understand 

 the principle of such a respiratory organ. The water 



1 " De metamorphosi Eleutheratorum, Bidrag. til Insekternes 

 Udviklings-historie." Pt. I. pi. iii., figs. 1—9. Kroyer. Naturh. 

 Tikskr. (1S62). 



