THE WATER CABINET. 131 
ments, of which the several parts are composed, are fre- 
quently so consolidated that it is difficult to detect or 
count them. For instance, the thorax, theoretically, 
consists of three segments; but, practically, the first of 
these is usually so largely developed as to appear to con- 
stitute the thorax in itself. The (theoretical) nine seg- 
ments of the abdomen are, in like manner, reduced to six 
or seven, in consequence of the last two or three being 
consolidated into one. . 
The order is an immense one, as to its range and 
variety, and hence there are in it many curious exceptions 
to the general conformation of a beetle. Some are utterly 
incapable of flight, owing to the non-possession of elytra, 
or wings ; some have elytra only ; and in some the elytra 
meet and unite along the suture; so that, if the insect 
had wings underneath, it would be impossible for it to 
use them. 
The specimens of coleoptera, kept in the water-cabinet, 
are among the most interesting of the whole collection, 
whether in the larva or imago form; and to this order 
we are indebted for a large number of aquatic species, 
that may be kept in jars, and some few that may be 
introduced without danger to the tank. 
Dytiscus MareGinauis is one of the handsomest of 
water-beetles, and its habits are amusing and instructive. 
It possesses an insatiable appetite, and great muscular 
power, as we soon discover when removing it from one jar 
to another, for if it succeeds in planting its claws firmly 
on the edge of the vessel, it is difficult to move it. It 
belongs to the large tribe of aquatic carnivora, ranged 
K 2 
