160 PHYSIOLOGY OF INSECTS. 



The lower lip or labium, u, closes the mouth below, as the 

 upper lip does above : it is a much more complicated 

 organ than the upper lip, and its variations afford excellent 

 characters for descriptions: it consists of four distinct 

 parts, which are obviously separated by sutural lines. The 

 insertion of the lower lip or insertio, u 1, is usually con- 

 cealed by the mentum below it, but occasionally projects 

 considerably beyond it, and becomes a part of some im- 

 portance. The true lip or labium proprium, u 2, is a solid, 

 horny plate, corresponding in character with the upper 

 lip : its variations are of great assistance to entomologists, 

 in determining the genus to which an insect belongs. 

 The third portion of the lip or palpiger, u 3, appears mostly 

 to rise from behind the second part, but is not unfrequently 

 continuous with it, and separated only by a sutural line ; 

 it is usually smaller, and of softer substance than the 

 second part, and is invariably to be distinguished by 

 bearing the feelers. The labial feelers or labipalpi, u, 

 originate one on each side of the palpiger, from which they 

 continue divaricating : these are composed of several dis- 

 tinct joints, of which the terminal one varies much in form. 

 The terminal portion of the lip or ligula, is always more 

 soft and fleshy than either of the preceding parts : it is 

 remarkable for the infinite variety of forms which it as- 

 sumes, and is the most certain guide in ascertaining insects 

 from description. 



An entire ligula or ligula Integra, is when its termina- 

 tion is simple and undivided; an entire ligula is either 

 obtuse or acute, truncate or rotundate, elongate or abbre- 

 viated. A bifid ligula or ligula bifida, is when there is a 

 deep notch down its centre, thus making the termination 

 double : a bifid ligula is usually very obtuse. A trifid 

 ligula or ligula trifida, is when it has three distinct termi- 

 nations ; this ligula is more variable in form than the 



