66 



INTRODUCTION. 



The larva of Gyrinus is very peculiar ; the mandibles are pro- 

 vided with a sucking canal as in Dytiscus,, and the larva, as a whole, 

 would superficially resemble a Dytiscid larva, were it not for the 

 long slender transparent tracheal gills with which the sides of the 

 abdominal segments are furnished ; each of the nine abdominal 

 segments bears one of these on each side, and the last segment 

 bears four, of which two may be re- 

 garded as cerci ; the stigmata are obsolete, 

 these gills occupying their places as 

 breathing organs ; they are also useful for 

 locomotion. The eggs of Gyrinus are 

 laid on aquatic plants and hatch in about 

 eight days ; when the larva is full-fed it 

 leaves the water and spins a whitish 

 cocoon on the stems of rushes or other 

 aquatic plants ; in about a month the 

 perfect insect emerges, and immediately 

 returns to the water. The cocoons of 

 Orectochilus have been found beneath 

 willow-bark a yard from the edge of a 

 river and two feet above ground. The 

 latter is a nocturnal insect and may be 

 seen gyrating in the moonlight ; in the 

 day it hides on or under logs etc. The 

 members of the genus Dineutes are large 

 flat insects, much larger than Gyrinus ; 

 in this genus the outer lobe of the maxillee 

 is entirely wanting. 



One of the most conspicuous species 

 of the family is the large Javan Porro- 

 rhynchus marginatus, which is top-shaped, 

 being broad and rounded behind and 

 gradually narrowed off to a triangular 

 and pointed head, the apex of the ab- 

 domen being furnished with four stout 



spines. 

 The 



Fig. 31 . — Gyrinus marinus. 

 Larva X 6. (After 

 Schiodte.) 



Gyrinid.u are widely spread 

 throughout the world and are probably 

 numerous in India; Gyrinus, Dineutes and 

 Orectochilus are all represented. The 

 position of the GyrinidvE has been dis- 

 cussed above (p. 50) ; the family is 

 retained here, as having distinct relations with the Adephagid 

 series, and especially with the Dytiscid^;, although it is certainly 

 abnormal. It seems, however, to be still more out of place in any 

 other section, and perhaps would be best treated as an entirely 

 isolated family. 



