46 DEFINITION OF THE TERM INSECT. 



and in the rest, with the above exceptions, it may be 

 distinctly traced. 



The head of insects is clearly analogous to that of 

 vertebrate animals, except in one respect, that they do 

 not breathe by it. It is the seat probably of the same 

 senses as seeing, hearing, smelling, tasting — and more pe- 

 culiarly perhaps of that of touch. The eyes of insects, 

 though allowed on all hands to be organs of sight, are 

 differently circumstanced in many particulars from those 

 of the animals last mentioned ; they are fixed, have nei- 

 ther iris nor pupil, are often compound, and are without 

 eyelids to cover them during sleep or repose ; there are 

 usually two compound ones composed of hexagonal 

 facets, but in some instances there are four ; and from 

 one to three simple in particular orders. The antenna? 

 of insects in number and in situation correspond with the 

 ears of the animals we are comparing with them ; but 

 whether they convey the vibrations of sound has not 

 been ascertained : that they receive pulses of some kind 

 from the atmosphere I shall prove to you hereafter — so 

 that if insects do not hear with them in one sense, they 

 may, by communicating information, and by aeroscopy, to 

 use Lehman's term, not directly in his sense 3 , supply the 

 place of ears, which would render them properly ana- 

 logous to those organs. That in numbers these remark- 

 able organs are tactors is generally agreed, but this is not 

 their universal use. That insects smell has been often . 

 proved ; but the organ of this sense has not been ascer- 

 tained. What has improperly been called the clypeus, 

 or the part terminating the face above the upper lip 

 {labrum), is in the situation of the nose of the Vertebrata, 



a Be Antennis Insect, ii. 65. 



