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Segments 8 to 13 are distinctl)' slenderer than the preceding ones, and are near]}- 

 equal to each other in length. All the segments, with the exceptions of the 

 first and second, bear two patches of sensor)' pits near the apex (PI. XVII. 

 fig. 5), one patch being placed on each side, and each pit bearing a very short 

 bristle. The number of pits is less on the pro.xiraal segments than on the distal 

 ones. The same sensory organ exists in Ilfinimeriis.* 



In our smaller specimens the antenna consists of but eight segments instead 

 of thirteen. The third segment is much longer than in the thirteeu-jointed antenna, 

 being about as long as the first segment. Segments 4 to 8 are each about two- 

 fifths the length of the third, the eighth being the shortest. A comparison of 

 the antennae of the large and small specimens proves that the increase in the 

 number of segments as the insect grows takes place in the region of the third 

 to sixth segments, Arixenia agreeing therein with the earwigs. The structure 

 of the segments is practically the same in the large and small specimens. I think 

 we may expect the adult Arixenia to have at least fourteen segments in the antenna. 



The mouth-parts present several characteristic points. The membrane con- 

 necting the clypens with the njaper lip or labrum is rather large and, like 

 most membranes connecting the sclerites witii one another, whitish and smooth, 

 bearing no hairs. The lahndu itself (Ir, PI. XVII. fig. 10 and PI. XVIII. fig. 1) 

 resembles that of the earwigs. It is transverse, with the angles rounded oft". 

 The anterior edge is feebly incurved and very slightly bent downwards, much 

 less so than in Hemimerus. The hind edge, seen from beneath in fig. 10 of 

 PI. XVII. , is straight, and the lateral angles are produced backwards. Numerous 

 longitudinal muscles are attached to the labrum, as indicated in fig. 1 of PI. XVIII. 



The mandible difl^ers remarkably from the ordinary type of insect mandible. 

 The right and left mandibles are practically alike. They are but little longer than 

 broad, and appear nearly flat (PI. XVII. figs. 3, 4). Both the upper and under 

 surfaces are convex along the centre and depressed at the inner edge. The upper- 

 side is more convex than the underside and bears a small patch of hairs at the 

 outer margin, while the under surface has no hairs at all. The inner and outer 

 margins of the mandible are rounded. As in the earwigs, the apex is armed with 

 three teeth, which remind one of the claws of a mammal, their apical surface 

 being convex and the pro-fimal surface concave. The whole inner margin i.s 

 densely clothed with bristles. This edge is quite narrow and is not at all suitable 

 for mastication, as it is in Ih'mimeras and Forficula. The bristles placed near 

 the apex of the mandible are thick, rigid, and somewhat curved in hook-shape, 

 whereas those of the more proximal portion of the edge are like ordinary bristles, 

 being longer and more flexible and becoming gradually thinner towards their tips. 

 The bristles are not placed in a single row, but stand closely packed on the whole 

 narrfiw surface of the edge of the mandible. It is clear from this peculiar armature, 

 which closely resembles that of the inner lobe of the maxilla of Arixenia, Forjicula, 

 and other mandibulate insects, that the food of Arixenia, or at least the way 

 of feeding, is ditt'erent from that of the earwigs. The mandibles of Hemimerus 

 and the earwigs have, as far as they are known, the ordinary triangular shape 

 with the inner margin incurved, as widely found in the mandibulate insects. 

 There may be earwigs which approach Arixenia in the structure of the mandibles. 

 Unfortunately these organs cannot be well seen without being dissected out, 



* Hansen, in Tiihkr. Knt. xv. p. 07 (1H94). 



