To the insect, order and disorder are exposed to sight 



and so we think to see the little emmets confer 



and locking their antennae immediatly transmit 



the instinctiv calls which each and all can feel; whereas 



the mutual fellowship of distributed cells 



hath so confounded thought that explanation is fetch' d 



from chemic agency; because in that science 



the reaction of unknown forces is described and summed 



in mathematic formulae pregnant of truth, 



and of such universal scope that, being calVd laws, 



their mere description passeth for Efficient Cause. 



— ROBERT BRIDGES 



Introduction 



The fundamental processes of vital activity, the ordered series of 

 physical and chemical changes which liberate energy and maintain 

 the 'immanent movement' of life, are probably the same wherever 

 'living matter' exists. The description of these changes is the ultimate 

 goal of physiology, of whatever group of organisms; but the tissues 

 of insects have been so little studied from that point of view, that in 

 this book we shall be concerned only with physiology on a humbler 

 plane: with the grosser functions of the organs and tissues, and with 

 the mechanisms by which these functions are co-ordinated to serve 

 the purpose of the insect as a whole. 



Of all the zoological classes, the insects are the most numerous in 

 species and the most varied in structure; the general physiology of 

 the group is therefore only too apt to be obscured by the endless 

 specializations of particular forms; and the main difficulty of a work 

 like the present is the exclusion of all that is special and non-essential, 

 and the retention of only that material which best illustrates the 

 general theme. There are, indeed, certain common factors which 

 condition the physiological make-up of the insects, and these factors 

 serve, to some extent, to link them all together into one system. They 

 are essentially terrestrial animals. This circumstance determines the 

 characters of their cuticle, and this, in turn, conditions their res- 

 piratory mechanism and the physiology of their growth. The respira- 

 tory mechanism and the cuticular skeleton are among the factors 



v 



