WATER-BEETLE. 



The female deposits her eggs about the beginning of spring, 

 each laying consisting of from forty to fifty eggs of a long and 

 cylindrical form, which are deposited in the water at random, the 

 larvae being hatched in the course of a fortnight. 



The larva of the dytiscus marginalis is very active, and casts 

 its skin, for the first time, when four or five days old. The second 

 moulting takes place after an equal interval, and as the insect 

 continues to grow, it casts its skin at intervals of about ten days. 

 The hide which it throws off may often be observed floating on 

 the water, with the mandibles, tail, and its appendages attached. 

 These larvce are of a dark ochre, or dirty brown colour, with the 

 body long and subcylindric, more slender at each extremity, but 

 especially towards the tail. The body consists of eleven seg- 

 ments, exclusive of the head. The first nine segments are some- 

 what scaly above, but fleshy beneath. The first segment is longer 

 and narrower than the following. The sixth, seventh, and eighth, 

 are larger than the others, which are of nearly equal size, and the 

 two terminal joints are long and conical ; the apex being slightly 

 truncated and scaly, with the sides fringed with hairs, whereby 

 the insect is enabled to swim along in the water, the action of 

 these joints being the same as that of an oar used in sculling a 

 boat. 



The terminal segment of the tails is provided with a pair of 

 long and slender pilose appendages, whereby the insect is enabled 

 to suspend itself at the surface of the water, which, as Swam- 

 merdam says, flows from them on every side, and thus the 

 suspension is effected. These appendages are tubular, and com- 

 municate with the air-vessels which run along the sides of the 

 body, which is moreover furnished with a series of spiracular 

 points, as shown in the figure. The head is large, rounded, and 

 depressed, and united to the first segment of the body by a short 

 neck, with five or six small elevated tubercles representing the 

 eyes. There are two' slender antennse, shown at a a in the 

 fig. 35, having a length nearly equal to the diameter of the head, 

 inserted in front of the eyes, and composed of seven joints. The 

 mouth is remarkably constructed, being destitute of the ordinary 

 aperture, so that the insect may be, and, indeed, has been, 

 described as wanting a mouth. 



The mandibles, which appear in the figure projecting from the 

 front of the head, are hollow, having a longitudinal slit near the 

 extremity, so as to enable the creature to suck through them the 

 juices of its prey, as a liquid is sucked through a straw or a quill, 

 the juices thus running down the mandibles into the mouth. 



The legs of the insect are long, slender, and ciliated on the 

 inside, serving as oars when swimming quickly. The body, 



89 



