76 EXTERNAL ANATOMY OF INSECTS. 



The feeler-bearer is seldom elongated without a similar elonga- 

 tion of the ligula. The ligula, or limb, is the fourth and ter- 

 minal portion of the lip ; its names have been most numerous. 

 Its variations in form are very striking, and afford excellent 

 generic characters. The two lips are united at their base. 

 The nearer we can approach to a perfect tetrapterous hexapod, 

 the more clearly will this be demonstrated. The type 1 of a 

 tetrapterous hexapod we may yet be unacquainted with. Such 

 a type must exhibit each organ fully developed. Our large 

 dragon-flies are the nearest approach we know of to full and 

 equal development of principal primary organs ; in these we 

 clearly perceive that the two lips are but a single piece, of 

 which the central portion is flexible and fleshy, and perforated 

 by a circular aperture, known as the pharynx. Let us now 

 trace the variations of the lower lip. 



In Lepkloptera, the lower lip is usually a triangular piece, 

 the base of which is closely united to the inferior region of the 

 skull. k Its surface is uniform, and its divisions obscure. Its 

 apex is generally acute, and terminated by a single point : yet 

 sometimes, as in Amaryssus, 1 it is bidentate. The labial- 

 feelers arise from it in nearly an erect position, one on each 

 side of the feeler-jaws, which form a small ring between them. 

 Although obscure, the divisions of the lip are manifest under a 

 good glass. The genus Inu, of Leach, exhibits very evident 

 lines across it, which show with sufficient accuracy the limits 

 of each division. The margin of the insertion rises to a level 

 with the anterior margin of the mentum. The labium is a 

 narrow arcuate piece, situated above this, and bordering 

 the insertion of the feelers. The feeler-bearer is another 

 narrow piece, whose margins, centrally, are nearly connate, late- 

 rally dilated for the reception of the feeler. The ligula is 

 very considerably larger than the other divisions of the lip : it 

 is triangular, with a very acute apex. The feelers in this 

 genus, as figured by Savigny, exhibit a basal joint, in addition 



1 By the word type I would imply the perfection of a peculiar kind. Hex- 

 apods, approaching spiders, or Ametobola, for instance, would be departures from 

 types. 



k Je dirai peu de choses de la levre inferieure : elle consiste en un simple 

 plaque triangulaire, ordinairement ecailleuse, unie par une membrane aux deux 

 tiges des machoires, et supportant a sa base les deux palpes que tout le monde 

 connait. — Savigny. 



1 Pnpilio Machaon. — Lin. 



