403 



have in Jacobson i on both the upper- and underside a few larger 

 pits with blackish rims, these pits being placed towards the base 

 on the proximal segments and nearer the apex on the distal ones. 

 The fourth segment is about one- third shorter than the third, 

 and this as long as the fifth in jacobsoni, while in esau the fourth 

 equals the fifth and both together are a little shorter than the 

 third. The relatively small number of segments and the lengths 

 of the antenna recall the higher Dermaptera or Eudermaptera 

 rather than the Protodermaptera. 



As the development of the mouth-parts and the gastronomy 

 of a species are interdependent, a comparison of these organs in 

 the two species of Arixenia is of special interest. If the habits 

 of csan and jacobsoni are really different, as the occurrence of 

 the former in the breast-pouch of Chciromcles and of the latter 

 as a free carnivore in a cave suggests, the mouth-parts must be 

 expected to differ, and, inversely, if they differ, we must con- 

 clude that the habits are not the same. The differences in the 

 mouth-parts are much greater than we anticipated. It is par- 

 ticularly the strong development of the mandibles as organs for 

 seizing the prey and cutting it up in which jacobsoni deviates 

 very widely 

 from esau, and 

 this develop- 

 ment carries 

 with it a corre- 

 sponding modi- 

 fication of the 

 other append- 

 ages. The large 

 mandibles are 

 covered by an 

 enlarged la- 

 brum, and the 

 greater length 

 of the labrum 



is compensated for by a corresponding reduction of the riipcus. 

 The proportional length and breadth of the labrum arc i : 2 8 

 in esau and i : I'S in jacobsoni, i.e. the upper lip is nearly three 

 times as broad as it is long in csait (text-fig. ij) and less 



Fu;. \2. — Upper lip oí .Irixciiia jacubioui. 

 Fig. 13. — Upper lip of .Arixenia aati. 

 ITiQ ]^. — Ninth abdominal stcrnitc of .1. jacobsoni ¿ 

 sp., support of penis. 



