4o6 



we have compared. The second feature which strikes one as 

 remarkable is the possession of three apical teeth instead of two. 

 A comparison with the other mandibles figured renders it evident 

 that the third tooth is the tooth placed in jacobsoni about the 

 centre of the mandible. This tooth is pushed apicad in conse- 

 quence of the excessive development of the setiferous portion 

 of the inner edge in esau. This portion of the edge is rounded, 

 and the distal bristles are modified into strong flexible spines, 

 which are curved at the apex. The bristles remind one strongly 

 of the maxilla, and there can be no doubt that the work the esau- 

 mandible has to accomplish diners in some essential point, pro- 

 ably in the kind of food to be seized and masticated, from the 

 work the Jacob soni-mandible has to perform. 



The remaining buccal organs (text-figs. 20, 21, 22) are 

 likewise diñerent in .4. esau and jacobsoni. The first maxilla 

 of jacobsoni is particularly distinguished from that of esau in the 

 armature of the inner lobe. In all Dermaptera (as far as they 

 have been examined with regard to their mouth-organs) inclusive 

 of Arixenia, the lacinia bears two apical teeth like the mandible, 

 excepting Hemimerus, which has four teeth. In jacobsoni these 

 teeth are almost conical, while they are concave beneath and 

 therefore more nearly shaped like the claws of a dog in A. esau. 

 The apical half of the inner surface is flat, with both the dorsal 

 and ventral edges cariniform and furnished each with a row of 

 bristles, there being no bristles in between these two longitudinal 

 rows, while the proximal portion of the inner surface is irregu- 

 larly covered with bristles. The lacinia (c i) of jacobsoni is 

 slenderer than in esau, its inner surface being concave with the 

 exception of the proximal portion, whereas it is convex in esau. 

 The apical teeth and the distal bristles are longer and slenderer, 

 and the dorsal seriated bristles are quite difterent from the 

 ventral ones, while the two rows are practically alike in esau 

 (text-fig. 20, c i). The outer lobe ( = galea) of the first maxilla 

 (c 2), apart from its larger size and the slightly increased number 

 of bristles in jacobsoni, agrees in the two species. The maxil- 

 lary palpus, however, is again essentially different, the bristles 

 being more numerous in jacobsoni, the segments much longer 

 and their proportions diñerent. Segments 2, 3, and 4 are of 

 equal width in esau (15 : 15 : 15), while in jacobsoni the fourth 



