HEAflPTERA. 263 



pearance and use from the mouth of gnawing insects, 

 ;t is found to he composed of the same or correspond- 

 ing parts, with the exception of the palpi, which are 

 quite ohsolete. These parts, however, have, of course, 

 undergone great modifications, to such a degree, in- 

 deed, that it is exceedingly difficult to recognise them. 

 It is only from their insertion and position relatively 

 to each other, that any agreement can he inferred ; 

 and, at most, the oral organs of suctorial species can 

 only be considered as analogous to or representative 

 of the parts of a mouth formed for mastication. There 

 is reason to believe that some of the ingenious ob- 

 servers, who have turned their attention to this sub- 

 ject, have carried their views rather too far, from a 

 wish to demonstrate a certain uniformity of organisa- 

 tion among different tribes an interesting inquiry, 

 but one which requires to be pursued with great 

 caution, as the fancy is so apt to lead us astray. At 

 all events, we have been often led from this cause 

 to the application of names, which, however signifi- 

 cant as originally used, becomes quite inappropriate 

 in their present extended acceptation. The term 

 mandibles, for example, is sufficiently descriptive of 

 the gnawing organs of the mandibulata, but is wholly 

 unmeaning when applied to a slender filet composing 

 a portion of a tube, in which both the form and the 

 function are completely changed. 



The rostrum, when not employed, is bent beneath 

 the breast, to which it is closely applied, passing be- 

 tween the legs. It consists of four joints, generally 

 distinctly marked, of a cylindrical form, or tapering 



