102 >ATUEAL HISTORY OF 



there is only one palpus attached to each blade of 

 the maxillae. These organs generally consist of four 

 joints, of which the terminal one is remarkable for 

 the variety of forms which it assumes in different 

 insects, affording valuable characters for distinguish- 

 ing genera. When an internal palpus is present, 

 it is usually formed of two slender articulations. 

 The palpi are susceptible of rapid and extended 

 motion, and are sometimes observed in a state of 

 intense vibration, similar to the antennas of Ichneu- 

 mons, and other Hymenoptera, when exploring a 

 decayed trunk to discover a proper nidus for the 

 reception of their eggs. They are supposed to con- 

 stitute one of the principal organs of touch. That 

 they perform this function is rendered extremely 

 probable by their structure, which is well adapted, 

 by its peculiar pliancy, to the examination of the 

 objects with which they come in contact. The 

 joints into which they are divided likewise favour 

 this explanation of their use, since they seem to 

 present some analogy to the articulated extremi- 

 ties which form the principal seat of the sense of 

 touch in the higher animals. It is at the same time 

 probable that these organs are subservient to other 

 purposes. 



As the mouth is covered above by the labrum or 

 upper lip, so it is closed beneath by the under lip 

 or labium. This part is situate between the max- 

 illae, and is composed, as it were, of two portions 

 joined together by their inner edges. The part 



