COLEOPTERA. 
127 
ment of the insects require it, the legs are adapted to various other purposes. 
Beetles that jump usually owe their leaping powers to the greatly thickened 
femora and straight and relatively long tibiae of the hind-legs. It would, however, 
be a mistake to suppose that when a beetle has thickened and strongly developed 
hind-legs it must consequently be able to jump. Some burrowing species, and 
others that are not very active in their movements, have very thick hind-legs ; 
though, as a rule, it is the front pair of legs which is thickened and otherwise 
modified to serve as digging organs in those beetles that burrow underground. In 
aquatic beetles the swimming legs are disposed like oars, and have all their parts 
broad and flat, while their breadth is further increased by rows of bristles. Either 
the hind-legs only, which is the rule, or the middle pair also, as in the whirligig 
beetles ( Gyrinidce ), may be thus transformed into swimming organs. The coxse, or 
basal joints of the legs, vary much in shape and in the mode in which they are 
inserted in their sockets on the under side of the thorax. Those of each pair are 
sometimes close together, sometimes widely separated from another; while a 
longer or shorter distance may intervene between the coxse of the different pairs of 
legs, and especially between those of the two hinder pairs. Considerable import¬ 
ance attaches to the number of joints in the tarsi or feet. In classifying beetles 
this number is one of the first things to be noticed. If a beetle has five joints in 
each of its tarsi, it is placed in that section of the order which is known as the 
Pentamera; if it appears to have only four joints in each foot, it belongs to the 
Tetramera; and if but three, to the Trimera. When there are five joints in each 
of the four anterior feet, and only four in the hind-feet, the beetle may be regarded 
as one of the Heteromera. To these general rules there are a few exceptions which 
need not be discussed here; but we must point out that although in the Tetramera 
the tarsi appear to be four-jointed, and in the Trimera three-jointed, they are really 
composed of five joints and four respectively. The fourth joint in the one case, 
and the third in the other, are, however, usually so small as not to be noticed 
except upon very close examination. The abdomen is never stalked in beetles, but 
attached to the thorax by a broad base, which is applied against the posterior 
coxse; exceptionally, however, as in certain mimicking species, its base may be 
more or less narrowed. It is generally somewhat flattened in shape: and on the 
upper side eight segments are usually distinguishable, which, so far as protected by 
the elytra, have a soft and but slightly horny integument. Five or six segments 
are generally visible on the ventral side, but in certain cases the number may be 
reduced. The terminal segments are usually retracted within the abdomen, and 
completely hidden from view, but in the females of many species they can be 
exserted in the form of a tubular ovipositor, which enables the insect to lay its 
eggs deep in the crevices of bark. 
Although beetles do not always exhibit differences in external form by which 
the sexes may be distinguished, such differences frequently exist, and are some¬ 
times of the most pronounced character. As a rule, the male is more slenderly 
built than the female, and has longer and more fully developed antennae; his eyes 
also are often larger, and in the length and shape of the legs, and in the width 
and structure of the tarsi, differences in the two sexes are frequently to be noticed. 
When the male is fully equipped for flying, the female may be without wings, or 
