THE DYTISCIDJE. ^97 



fly ; and they are frequently noticed to crawl out of the water, 

 and to fly from one pond to another. They thus appear to lead 

 two lives : one, the ordinary sub-aerial existence of beetles ; and 

 the other the special life of water insects. They are made like 

 land beetles ; and they are therefore obliged to come to the surface 

 every now and then in order to breathe, and a very simple arrange- 

 ment enables them to obtain a fresh supply of air. The spiracles, 

 or breathing organs, are situated on the upper part of the body, 

 and are protected by the elytra, or wing cases, which fit the upper 

 part and sides of the body, so that no water can get underneath 

 them. When the insect wishes to breathe, it lets itself float to 

 the top of the water, so that the upper part of the back projects 

 above the surface ; then the elytra are raised up, expiration takes 

 place, and a supply of fresh air is inspired, and then the beetle 

 shuts down the wing-cases, and includes beneath them a certain 

 quantity of air, which it uses from time to time. 



The DytiscidcB are carnivorous, and attack all kinds of aquatic 

 insects, which they tear and injure with their strong mandibles. 

 Their larvae live in the water, and have the same propensities 

 as the adults ; and they are constantly chasing a number of insects, 

 mollusca, and even young fish. They are long creatures, nar^ 

 rowed behind, and are clothed in such a hard integument that they 

 may be said to be truly armoured. Their head is large and 

 broad, and the mouthpieces project ; their mandibles are arched, 

 and are perforated at the extremity, so that the insect can suck 

 through them ; and their legs are long. They are very active, 

 and swim readily by means of a flexible abdomen, which is ter- 

 minated by two appendages, which are often leaf-shaped. 



These insects are provided with spiracles on the sides of all 

 the abdominal segments ; nevertheless, when they come to breathe 

 on the surface of the water, they lift up their tails where the last 

 spiracles are, and appear to respire with them in particular. When 

 about to undergo their metamorphosis, they come out of the 

 water, and hide themselves in the mud or sand by its side, and 

 make a cell according to their size, and are transformed into 



nymphs. 



The commonest kind is Dytiscus marginalis, and it abounds 



in all the stagnant waters of Europe. 



