STRUCTURE OF THE THORAX. 19 



groups of insects are most astonishing ; in some cases 

 they are considerably longer than the whole body^ 

 whilst in others they appear like scarcely perceptible 

 tubercles on the front of the head^ and between these 

 two extremes we meet with them in every degree of 

 development. That these organs have some import- 

 ant functions assigned to them cannot be doubted_, but 

 what these may be is by no means so certain. They 

 have been regarded by some entomologists as organs 

 of hearings by others as organs of smell, and a few 

 have endeavoured to get rid of the difiiculty by sup- 

 posing them to be the seats of some sixth sense of 

 which we have no knowledge. At present, however, 

 we have no satisfactory proof of the offices performed 

 by the antennae in the ifisect oeconomy. 



The Thorax. — We have travelled so far from the 

 original definition of an Insect with which we started 

 on our jom-ney, that it may be necessary to remind the 

 reader, that of the thirteen segments forming the body 

 of one of these creatures, the second, third and fourth 

 compose a separate region, intermediate between the 

 head and abdomen, and denominated the thorax, or 

 chest. These three segments differ in construction, 

 not only from the other segments of the body, but 

 also amongst themselves; they are usually separate, 

 but in many cases so completely united together, that 

 the boundaries of the individual segments cannot be 

 distinguished without difficulty. Each segment is 

 found to be composed of several plates united together 

 at their edges, and to these, as to the segments them- 

 selves, different names have been given by entomolo- 

 gists, although in the present instance it will be un- 

 necessary for us to go very deeply into this part of the 

 subject. All that requires to be stated here is, that 



