i 3 4 INSECTS. 



is swimming about under the water ; but the air meanwhile is being used up in 

 breathing by means of the thoracic and abdominal spiracles. The beetles fly 

 strongly, and on fine summer evenings may sometimes be seen winging their way 

 to new quarters, a change which is often necessitated by the drying up of the pools 

 in which they had previously been living. Dytiscus ma >y In alls, one of the largest 

 British species, is also one of the commonest and best known. Another common 

 species, Acilius sulcatus, is also represented in our figure. 



The Gyrinidce, or whirligig beetles, are a small but very well-defined group, and 

 in many points of structure are sharply distinguished from the other families of the 

 tribe Adephaga. In their oval shapes they resemble the Dytiscidce, though they are 

 usually somewhat flatter below and a little more convex on the upper side. But in 

 the relative proportions of the three pairs of legs they are 

 entirely different. The fore -legs are long and slender, and 

 when stretched out look like arms, whereas the two hinder 

 pairs are short and broad, being modified for use as paddles in 

 swimming. Another very distinctive feature is presented by 

 the eyes, each of which is divided by a ridge on the side of the 

 head into two widely separated portions, one lying on the upper 



whirligig s i,] c f the ] lea j an( j tne ot h er underneath. These beetles 

 beetle, Gyrivms . ...... 



natator (enlarged). appear, in consequence, to have four eyes ; one pair, as it is said, 



though there is no proof of the fact, for espying objects above 



them, the other for looking at things in the water below. From the Dytiscidce 



and GarabidcB they differ further in having their antennas shorter than the head, 



and the outer lobe of the maxillaa either completely atrophied or else in the form 



of a slender spine. The Gyrinidce, though widely distributed and represented in 



almost all parts of the world, include altogether rather less than three hundred 



known species. The genera are few in number and two only occur in Europe. 



Some of the British species, such as Gyrinus natator, are commonly to be seen in 



ponds and canals or " holes " in reedy sluggish streams, where the shiny little 



beetles attract attention by the ease and rapidity of their movements as they skim 



about on the surface of the water, performing a variety of intricate evolutions, 



some sweeping along in graceful curves, others going round in circles or spiral 



tracks, now all collecting together in groups, and then, if startled, suddenly darting 



off with amazing speed in every direction. 



The next beetles we have to consider are those which, on account of their 



abbreviated wing-cases, are known as the Brachy elytra. This tribe to which, 



however, not all beetles with short elytra belong, contains a single very large 



family — the Staphylin idee. Owing to the shortness of their elytra, and the usually 



narrow and elongated form of their bodies, the rove-beetles have an easily recognised 



and characteristic appearance. The head is generally large and flat with a narrow 



neck behind where it fits into the prothorax. The antennae — composed of eleven, 



or occasionally twelve joints — are usually filiform, but are often slightly thickened 



towards the extremity, and in some cases end in a distinct club. Though prominent 



and conspicuous in a few genera, the eyes are, as a rule, raised but very little above 



the general surface of the head. It is interesting to note that ocelli, which are of 



such rare occurrence in adult beetles, are to be found in certain groups of this 



