72 THE BIOLOGY OF INSECTS 



the creature is exceedingly sensitive to impressions derived 

 from objects touched. Sensory hairs and spines are also 

 often present on the cuticle of various segments of the body, 

 especially in the case of those insects whose exoskeleton is 

 relatively weak, so that prompt response to impressions from 

 all quarters is essential to secure safety. Many insects, as 

 they walk or run, may be seen to keep the tips of their 

 feelers in continual swaying movement, which has the effect 

 of bringing the sensory hairs on the segments of the feelers 

 in such relation v^dth surrounding objects that there are 

 abundant possibilities of varied points of contact. And the 

 response of the whole insect to the impressions thus received 

 depends upon the positions of the various sensory hairs 

 where these impressions are started through contact with 

 external objects. 



The nerve- endings affected through such hairs are 

 termed tactile, and their mode of action suggests that insects 

 possess a '' sense of touch." It is certain that these nerve- 

 endings are affected when the hairs within which their 

 extremities He come into contact with outside objects, and 

 the insect's reaction to such stimulation, due to muscular 

 contraction, shows that a reflex impulse travels to and from 

 the central nervous system. So far there is analogy between 

 what happens in the insect and in a human being. But 

 what we understand by a sensation which leads us to 

 distinguish an object as hard or soft, rough or smooth, is 

 essentially a conscious experience, accompanying certain 

 nerve-impulses, but not identifiable with them. We are 

 not, therefore, able to assert that an insect *' feels " as we do. 

 Indeed, the insect's tactile nerve-endings are in form very 

 different from those of vertebrates and are affected in a 

 different manner. A tactile corpuscle of the human finger, 

 for example, is situated beneath the outer skin (epidermis) 

 and is affected indirectly by variations of pressure or resist- 

 ance acting at the surface of the skin yet able to " irritate " 

 the nerve-ending, though the latter lies under many layers 

 of cells. The insect's tactile nerve-ending is, as we have 

 seen, prolonged so as to rest within a narrow hair ; it is 



