108 MODERN CLASSIFIiiATION OF INSECTS. 



abling them to change their abode without difficulty, when the drying 

 up of their native pool compels them to emigrate. This will enable us to 

 account for the occasional discovery of these insects in small puddles 

 of newly-fallen rain-water. The structure of the short hind legs, and 

 especially of the curious branched tarsi, must be examined, in endea- 

 vouring to account for the singular motions of these insects * ; the as- 

 sembling together of which has been regarded by some writers as 

 resulting purely from a strong social influence, and by others, as indi- 

 cating no closer bond than that of animals congregating round their 

 common food. That the food of the Gyrinidse consists of small 

 dead floating insects, I have ascertained ; but I would further 

 suggest that, being produced on the same spot, as is the case with 

 the swarms of midges, they are influenced, in some degree, by the 

 common desire of continuing their species. I have often ob- 

 served that, in their gyrations, they hit against one another. In dull 

 and inclement weather, they betake themselves to quiet places, under 

 bridges, or beneath the roots of trees growing at the water's edge. 

 When touched, they emit a disagreeable odour, arising from a milky 

 fluid, which is discharged from the pores of different parts of the body, 

 or, according to De Geer, from the two minute retractile lobes at its 

 extremity. It seems not improbable that this fluid, united with 

 the high polish of the body, may have the effect of resisting the 

 action of the water. It appears, however, that G. minutus and O. 

 villosus are scentless. (^Kirhy and Spence, ii. 242.) The remarkable 

 structure of the eyes, which, unlike those of the majority of insects, 

 consist of two distinct pairs, one on the upper, and the other on the 

 lower, surface of the head, must be greatly serviceable to the insect in 

 the peculiar situation in which it is generally observed, and whereby 

 it is enabled to see objects beneath it in the water, and above it in 

 the air. 



The female, shortly after impregnation, deposits her eggs, which are 

 small, and of cylindrical form, and placed end to end, in parallel rows, 

 upon the leaves of aquatic plants ; and from which, at the end of eight 

 days, the larvae are produced. De Geer {JSItmoires, vol. iv.) and Rosel 

 {Ablmndl. vol. iii. suppl. tab. 31.) succeeded in obtaining these larvae 

 from eggs deposited by the females ; but Modeer (3Iem. Acad. Reg. 

 Siiec. 1770) is the only author who has traced the insect through 



* <' Mr. Briggs observes, that the G. natator moves all its legs at once with 

 wonderful rapidity, by which motion it produces a radiating vibration on the surface 

 of the water." — A', and S. ii, 361. 



