THE DOMINANT INSECT 5 



this is an important point) it has proved capable of limit- 

 less adjustment and alteration : so that at the present day 

 we find insects feeding upon and digesting almost every 

 substance from which nutriment can be extracted. 

 Beneath the digestive canal (not above it as in the case of 

 vertebrate animals) passes the central nervous chain of 

 the insect. This is composed of twin cords which connect 

 a series of paired knobs, called ganglia. Roughly speaking, 

 each pair of ganglia may be likened to a minor brain 

 which governs the activities of the parts that immediately 

 surround it. This arrangement accounts for the curious 

 disconnectedness of action which is observable in a maimed 

 insect. The brain within the head innervates the eyes 

 and antenna?, and is, as it were, the centre of will-power 

 in regard to the movements of the wings and legs. Thus, 

 an insect deprived of its brain cannot go to its food, 

 though it is able to eat if food be placed in contact with 

 its mouth — the explanation being that the actions of 

 the mouth are regulated by one of the minor brains. 

 Again, although the brainless insect cannot move intelli- 

 gently in a given direction, it remains capable of aimless 

 locomotion. Deprived of its head, it can walk or fly for 

 hours, possibly until starvation supervenes. Similarly, 

 the detached abdomen will long continue the muscular 

 movements incident to respiration, just as though it were 

 still part of a complete organism. 



A recapitulation of the foregoing points will serve 

 to emphasize the fact that the typical insect possesses 

 a combination of qualities eminently calculated to com- 

 mand success. Firstly, insects stand firmly. Their six 

 legs, a double tripod, afford the best mechanical base 

 of support. In walking or running the legs are moved 

 forward in sets of three — the first and third legs on the 

 one side, the second on the other ; so that a tripod always 



