THE ANATOMY OF THE STAG BEETLE. 
15 
ever, entering in detail on our subject, it will be well to call to 
mind the principles which determine not only the rank of 
insects in the Articulate series, but that also of the different 
orders of insects among themselves ; so shall we be able to view 
the structures presented to our notice, not as a piece of isolated 
animal mechanism, but as one holding its special place among 
others closely allied to it — an example not only of insect structure 
in general, but of coleopterous structure in particular. The 
Articulate type, under which Cuvier ranged all those animals 
whose bodies are composed of a number of successive rings or 
segments, includes the three great divisions of the Worms, 
Crustaceans, and Insects ; and these take rank among themselves 
in proportion to the amount of specialization of function ex- 
hibited in their organization. This principle has been aptly 
termed by Milne Edwards as that of the physiological division 
of labour. The various actions and processes of life termed 
functions may be carried on, as in that simplest of all animals 
•the Amoeba, indifferently by any part of the body, or each 
function may have a special part of the body allotted to it ; and 
in proportion as this is the case the various functions will be 
carried on with greater or less perfection. More especially is 
this seen with respect to the two great functions of animal life, viz. 
locomotion and sensation as opposed to the purely vegetative ones 
of nutrition and reproduction. It is the perfection of these 
functions which places so broad a stamp of superiority on the 
higher Articulate classes, viz. the Crustacea and Insects, as com- 
pared with their humbler brethren the Worms. 
The result of this specialization of function, as exhibited in 
the body of an articulate animal, is chiefly its more and more 
perfect differentiation into the three regions of head, thorax, and 
abdomen ; to the first belong the functions of sensation, to the 
second those of motion, and to the third the vegetative functions 
of nutrition and reproduction. The original division of the body 
into somewhat similar rings becomes subordinate to a new 
division into regions ; and the more clearly this is observable, 
the higher rank will the animal exhibiting it take. 
In intimate connexion with the alterations thus apparent in 
the external form, there is observable a concentration of the 
nervous system towards the head and thorax. In its simplest 
form which obtains in the Worms, this system consists of two 
longitudinal cords, each with a swelling (nerve-knot, or 
ganglion), corresponding to each segment. In the Diptera, as 
an example of one of the higher Insect orders, we find this 
chain of ganglia reduced to two — one in the head and one in 
the thorax, — the abdomen being supplied only with filaments 
from the latter. It is almost needless to point out how this 
concentration of the nervous system towards the head finds its 
