10 BRITISH INSECTS 



two distinct threads running within the lower, or 

 ventral, wall of the body its location being thus 

 below the digestive canal, not above it, as is the case 

 with a fish, a reptile, a bird, or a mammal. In each 

 segment the twin threads were swollen, forming 

 paired knobs, or ganglia ; and each ganglion consti- 

 tuted a kind of " brain " which governed the affairs of 

 its own immediate surroundings, but was little con- 

 cerned with those of neighbouring segments, albeit a 

 certain amount of nervous exchange would take place 

 to insure perfect co-ordination of the various bodily 

 functions. So, at least, we may figure the nerve- 

 mechanism of the primitive insect ; and even to-day 

 the same principle obtains, although in most modern 

 insects the mechanism itself has been greatly modified, 

 many of the originally separate ganglia being incor- 

 porated. One such mass, called by courtesy " the 

 brain," is found in the front part of the head. It is 

 connected by nerves with the eyes and the antennae, 

 and exercises a kind of controlling influence where 

 movements of the legs and wings are concerned. 

 Yet a brainless insect can walk or fly in an aimless, 

 erratic manner, because the actual motor nerves, 

 which send stimuli to the muscles of the legs and 

 wings, go to ganglia in the thorax ; it can also eat if 

 food be placed in contact with its mouth-parts, the 

 reason being that the nerves from the latter and their 

 palpi are connected with a ganglion (next behind the 

 brain) situated beneath the gullet. 



In view of these facts, it is scarcely surprising to 

 learn that insects are lacking in intelligence. True, 

 some of the more highly organized kinds appear to 

 " remember," and to profit by experience to a limited 

 extent ; but in most of their actions insects are mani- 



