I AQUATIC BEETLES 61 



of these draw air from the supply which is lodged 

 beneath the wing-covers, and this they can do at all 

 times even if the Beetle is submerged. 



When a Dytiscus is captured, it often discharges 

 a milky fluid from the thorax, just behind the head. 

 The fluid smells like sulphuretted hydrogen ; whether 

 it has any peculiar taste or not, naturalists have not, 

 I believe, tried to ascertain. At the tail-end again 

 are two anal glands which can suddenly discharge 

 an unpleasant ammoniacal fluid of yellow colour, 

 and this, there can be little doubt, is a startling 

 proceeding, which may often cause a bird to drop 

 the Beetle which it has seized. 1 The white fluid is 

 most abundant in fresh-caught specimens ; the yellow 

 fluid in captives. 



The Dytiscidae are long-lived and have been kept 

 several years in captivity. 



THE GREAT WATER-BEETLE (HvDRorniLus). 



The Great Water-beetle, Hydrophilus piceus, has 

 attracted the attention of spme of the most eminent 



1 Many Carabidas and some other Beetles, e.g. Timarcha, 

 eject a fluid, often of unpleasant odour, from the mouth, when 

 first captured. Brachinus discharges a pungent and explosive 

 liquid from the anus. Cantharis, Meloe, Gyrinus. etc., emit a 

 fluid from the leg-joints. Ilybius fuliginosus emits a strong- 

 smelling fluid. Ponds containing the Beetle can be distinguished 

 by the smell, even if the Insect is not visible. Gyrinus, besides 

 the fluid emitted from its joints, secretes a sticky white paste, 

 of pungent odour, from its tail. It is probably this which is 

 used to fasten the eggs to leaves. 



