130 THE CAUSES WHICH PROPAGATE 



running from the membranous penultimate dorsal arc. The 

 raised teeth in Elaphrus idiginoms (Fab.), and ciqyreus, (Dufr.), do 

 not stand close together, being separated by intervals of a tooth. 

 Their numbers do not appear to exceed ten or twelve. The 

 teeth in B. muUipunctata are similar, but B. rij)ariu8 has them 

 closer placed, and twice as numei'ous. At the bend of the wing- 

 covers before the ai:)ex are placed the passive organs of stridula- 

 tion, in the form of a raised, somewhat convex, and wrinkled 

 callosity (•«), \vider anteriorly, and gradually attenuated back- 

 wards. The stridulation of a Ceylon ground beetle {Cerapterus 

 latipes, Swed.), has been recorded by Mr. Thwaites. Many other 

 exotics are, with little doubt, musical. 



The Water Beetles [Hydradephaga) the summer idler by the 

 silent pool sees rise to the surface, hang for a moment suspended 

 with their head downwards, and then, having secured a silvery 

 globule of air, dive seal-like down through the slimy abyss, at 

 first sight, from an oval form common to aqueous life, seem more 

 akin to shell-fish than insecta ; and yet these amphibious 

 creatures are really ferocious, voracious beings, differing in no 

 essential from the ground beetles, distinguished alone by a slight 

 modification of certain parts, suflicing to adapt them to their 

 abode. Although they thus rise and sink at intervals during 

 the day, for the sake of breathing atmospheric air, it corresponds 

 to the period of sleep and dreams, their time of activity being 

 the evening twilight or shadow of night, when they not im- 

 commonly, leaving the pool, take wing, and traverse swiftly 

 the air, to found new colonies and to populate new waters. 



Pelohius Hermanni (Fab.), a smallish red Water Beetle, some- 

 what plentiful in stagnant ponds on the clayey district surround- 

 ing London, where it delights to grovel in the mud or cling to 

 the weeds, utters a sharp noise on capture, when escaping the 

 grasp of a Water Scorpion, or when fighting a rival, when it like- 

 wise exhibits some of that pugnacious temper characterising the 

 stickleback fish. Mr. Douglas says that on this subject a friend 

 writes as follows : — " Of the beetles popularly knowTi as ' screech 

 beetles,^ I have several in my aquarium, which contains more 

 than twenty gallons of water, and I have heard the peculiar 

 noise emitted when two beetles were quarrelling for a piece of 

 worm. I think the noise came from two at the bottom, but as 



