THE CARNIVOROUS WATER-BEETLES. 



311 



/ 



HALIPLUS Ft'LVUS. 



(episternum) in the greai, majority of the true Dyticidse is extended so as to form part of the orbit of 

 the socket ; but in Haliplinse, as in all the Carabidse, it is not. The Haliplinse are, notwithstanding, 

 essentially Water-beetles, and cannot be classed with the Carabidse ; they swim freely, though 

 somewhat slowly and with an ambulatory motion through the water, and their 

 hind legs, although not compressed and flattened into oar-like organs, 

 are furnished with a fringe of long hairs, unlike anything presented 

 by the Carabidse, which assists them in their motion through the 

 water. 



ijnj| y^|:| \ The true Dyticidse form three sub-families, the family type 



j ;i;ff ; .y\ * reaching its highest degree of development in the genus Cybister, in 

 ft)'/ It which the enormously expanded hind haunches are soldered to a 

 metasternum of voluminous dimensions. They are found chiefly in 

 tropical and sub-tropical countries. The genus Dyticus, consisting 

 of insects nearly as large as those of the genus just mentioned, YARIEGATUS. 

 inhabits chiefly temperate, and even high, northern latitudes. Six 

 species are found in Britain, Dyticus marginalis being one of the commonest pond insects, and 

 the favourite tenant of many a juvenile aquarium. Laccophilus, a genus of smaller species, two 

 of which are common in every English pond, have remarkably well-developed hind legs, and are 

 excellent swimmers. The genus is widely distributed in all climates ; the same is the case with 

 Jlydroporus, of which no fewer than fifty species have been found in Great Britain ; but Suphis, and 

 other allied genera, are confined to the tropics. 



FAMILY GYRINIDJS, AND THE ANOMALOUS FAMILY PAUSSID.E. 



The Gyrinidce, or " Whirligig Beetles," of the surface of our ponds and rivers, form the last 

 family of Adephaga, and consist of a comparatively small number of genera and species, varying but 

 little from a common type. They differ from the rest of the Adephaga in the absence, or where 

 present, the slender, unjointed form of the external lobe of the maxilla, and in the possession of four 

 eyes, the eye on each side being divided into two, one situated above for vision in the air, and the 

 other below for espying what happens in the watei*. From the Dyticidse, with which they agree in 

 general form and habit, and in most parts of the structure of the mouth, they differ in their legs, the 

 relative development of which is reversed, as it is here the anterior pair which are longest, whilst in 

 Dyticidae it is the hindmost. The two hinder pairs of legs are extremely short, broad, and compressed, 

 modified, in fact, to suit their extraordinary mode of locomotion a rapid skimming incurves or circles 

 over the surface of the water. The rapid forward motion is produced by the quick fore-and-aft 

 movement of these strong and well-knit members, and the curves by the long anterior legs, which, 

 usually kept folded under the breast, are jerked out one at a time, so as to change 

 the straight line of progression into a curve. When alarmed, they plunge into the 

 depths of the liquid element, carrying with them a relatively large air-bubble to 

 supply their needs until they return to the surface. The females 

 lay their eggs on the leaves of aquatic plants, and the larvae which 

 emerge from them are remarkable for their general resemblance to 

 small Centipedes, owing to the abdominal segments being furnished 

 on each side with a slender conical process resembling legs, 

 terminal, or ninth segment, having four of these appendages, longer 

 and more movable than the others. As these curious processes 

 have been found at least, the apical ones to have a fine trachea, 

 or air-tube, passing through them to their apex, they are supposed 

 to serve as breathing organs. 



Gyrinidse are generally distributed over the earth, but, as already observed, the type is but 

 little varied. The common British species (Gyrinus natator) is a fair representative of the whole 

 family, the most remarkable species of which are the Porrorhynchus marginatus of Java, with its 

 long and triangular upper lip, giving a snout-like appearance to the front of the head, and the 

 Enhydrus sulcatus of Brazil, more than three-quarters of an inch in length. The Gyrinus distinctly 



HYDROPHORUS GKisEo- 

 STRIATUS. 



8upHIS CIMI _ 

 COIDES. 



