NATURAL HISTORY. 

 194 



living in streams and ponds. Each larva constructs a case to protect its 

 soft body, and, protected by these, they crawl about over the bottom In 

 Lne and material there is a great difference in these cases, as is shown 

 bv L ffgures. Some cement grains of sand together by means of a sdky 

 substance; others use sawdust, snail-shells, dead leaves, pine needles or 

 any t hing hey may run across to make their cases ; and one form builds a 

 s,,h-al else, almost the exact counterpart of the shell of a snail Indeed, 

 naturalists have made the mistake and described these shell-like cases as 

 the shells of new species of molluscs. These caddis-worms are carnivorous 

 and live upon the smaller and even microscopic forms of animals which 

 inhabit the same waters. The perfect insects resemble to a considerable 

 extent some of the moths, and it may be that here is to be sought the line of 

 descent of these higher forms. 



Beetles. 



The beetles form by far the largest group of the animal kingdom, the 

 number of species possibly equalling those of all of the other groups 

 together. Two German students, Gemminger and Harold, published, a lew 

 years a-o, a catalogue of all the described species of beetles. It contained 

 over seventy-seven thousand names ; but it of course could not be com- 

 plete Making due allowance for omissions, and for species described since 

 the publication of the catalogue, there must be considerably over a hundred 

 thousand species of beetles described, and there are thousands more in col- 

 lections waiting to be worked up. It is only in Europe and the Eastern 

 United States that we have any adequate knowledge of our insect forms, 

 and even in these much-explored regions new species are continually turn- 

 ing up. In the United States, which is comparatively poor in species, the 

 Last catalogue (by Mr. Samuel Henshaw) enumerates 9789 species, and 



there are still many more to be described. In the pres- 

 ence of such numbers as these, one at once sees how 

 impossible it is to have common names for all the species. 

 The beetles have strong jaws, well adapted for bitmg, 

 and two pairs of wings, the first pair of which forms 

 a hardened sheath for the other pair, which alone is of 

 use in flight, This ensheathing has given rise to the 

 scientific name of the group Coleoptera, which is derived 

 fig. 181. -a ti S er-bee- f rom the Greek for sheath-wing. When at rest (the con- 



tie (Tetracha). „ . ,. , •^™ c . 



dition shown in most of our figures), these outer wings 

 elytra, they are called — are folded on the back, perfectly concealing th 

 thinner ones, which are compactly folded below. In flight the wing-covers 

 are held elevated over the back, while the under pair are rapidly vibrated; 



