206 FBESH-WATEE AQUAEIA. 



themselves to the back of the abdomen beneath the elytra, 

 and they are, we may conolnde, breathers of atmospheric air. 

 D. mcvrginalis is also subject to parasitic fungus (Saprolegnia 

 ferox), which I believe is not nearly so fatal to beetles as it 

 is to fish. 



The male D. marginalis is so unlike the female that some- 

 times they have been taken by the inexperienced as members 

 of different species. These beetles are about an inch long, 

 oblong-ovate in shape, and olive-brown in colour. The margins 

 of the thorax and elytra are marked with a yellow band. 

 There is also a rather indistinct yellow crescent in the apex 

 of the latter. The males are distinguished by having the 

 first three joints of the fore tarsi developed into a round 

 sucker, and by having smooth elytra; whUe the females have 

 no widening of the tarsi, and possess wing cases which are 

 furrowed or sulcated. The eggs of these beetles are laid in 

 slits made in the aquatic plants by the help of a contrivance 

 called an ovipositor, possessed by the female, and are hatched 

 in about a fortnight. 



The larva of D. marginalis (Fig. 132), when full-grown, is 

 about 2in. long. It is such a rapacious creature that it has 

 received the names of "Water-Devil" and "Water-Tiger," 

 while its shape has given it the title of " Fresh-water Shrimp." 

 The body of the animal, is a dirty brown in colour and 

 elongated in shape, and gradually tapers towards the tail. 

 There are six legs and eleven segments, the former being 

 affixed in pairs to the first three of the latter. At the 

 extremity of the last segment there are two appendages 

 fringed with hair, and close to these appendages are two 

 spiracles, or breathing holes, by means of which the animal 

 respires atmospheric air. The spiracles at the sides of the 

 body, not being required at present, are unopened. The larva 

 is furnished with some terrible-looking sickle-hke jaws, which 

 are hollow, and through them it is able to suck the juices of 

 its captives. It also possesses undeveloped palpi and antennaj. 



The Water- Tiger is a great eater, having, if possible, a 

 larger appetite than its parents. It seizes its prey with its 

 jaws, and, with head thrown back, extracts its food. The 



