70 THE BIOLOGY OF INSECTS 



still more, intentions and apprehensions like our own, we 

 quickly pass into regions of speculation, as we can no longer 

 be guided by carefully tested fact. An insect may react 

 to its surroundings in somewhat the same way as a man 

 reacts, but it is not justifiable to infer from this that the 

 insect's state of consciousness is like the man's. The 

 questions thus raised are interesting, even fascinating, 

 despite their difficulty. Before attempting to discuss them 

 it will be well to consider in detail some examples of the 

 working of stimulation and response in the insect's body. 



A brief general sketch of the insectan nervous system 

 has been already given in the first chapter (pp. 7-10) of 

 this book, and it was there mentioned that movements such 

 as the moth's flight towards a lamp or towards a female of 

 his kind shut up in a box, movements clearly to be regarded 

 as responses to stimulation from without, are called reflex 

 actions. In a reflex action some nerve-ending, usually near 

 the body surface and capable of being stimulated through a 

 specialised region of the cuticle, is aflFected so that it transmits 

 through a nerve-fibre an impulse to a nerve-centre such as 

 part of the brain or a ventral ganglion. From the nerve- 

 centre the impulse is then reflected along other nerve-fibres, 

 whose endings in contact with muscle-fibres, impel these to 

 contract and thus give rise to visible movement. Such 

 movement is the result of, and to the observer affords 

 evidence for, the transmission of the nerve-impulse to and 

 from the nerve-centre. Impulses towards the centre, as 

 well as the fibres along which they travel, are usually defined 

 as aff"erent, while impulses from the centre to the muscles 

 and also the nerve-fibres conveying them are called efferent. 



An insect's nervous system may be regarded as a vast 

 complex of living cells from each of which processes branch 

 in various directions, many of these processes passing into 

 the axes of nerve-fibres. In every nerve-centre a number 

 of cells are grouped, and the fibres, whose axes are the 

 prolongations of these cells, are bound into the white 

 thread-like cords, evident on dissection, which are called 

 nerves : every nerve is a bundle of many fibres. A nerve- 



