420 



frontal surface of the clutch (clu). The ejaculatory duct projects 

 from the opening at od. The broad hook of bar B- is hollow, 

 beneath and dentate, and catches hold of the apical margin of 

 the left eighth sternite from the upperside. The hooks of 

 B^ and B", standing opposite one another and facing opposite 

 directions, secure a very firm hold (cf. text-figs. 27 and 28). 

 Moreover, the apical hook of B* grips the apex of the clutch C 

 of the female from above, pressing it down, counteracting the 

 strain exercised by the hook of ß' and thus preventing this 

 hook from slipping off the anterior surface of the clutch. The 

 bar B^ lies against the margin of the right half of the eighth ster- 

 nite. The parameres (par) do not play any part in holding the 

 female. They appear to be, in Arixenia, tactile organs rather 

 than claspers. Their soft texture and minute papillae-like hairs 

 point in that direction. 



The above-mentioned embryos, which have already a coat 

 of brown hairs, are curled up in the usual way, the callipers 

 lying on the frons at the inside of the antennae. The length 

 in a straight line from the vertex to the farthest point of 

 the abdomen is 4 mm., the total length from the upperlip 

 to the pygidium measured along the back being about 10 mm. 

 Allowing for further growth of the embryo and, on the other 

 hand, for the telescoping of the segments when the embryo is 

 born and straightened out, the length of the young larva, apart 

 from the antennae and callipers, may be estimated at from 10 to 

 12 mm 



This short survey of the morphology and anatomy of the 

 adult Arixenia jacohsoni confirms our opinion that the insect 

 stands apart from the other Dermaptera, the main distinctions 

 being the great reduction of the eyes, the full number of abdominal 

 segments in the female as well as in the male and larval stages, 

 the primitive form of the callipers, the unique structure of the 

 male genitalia, and ovarial pregnancy. To these characteristics 

 may be added, as of secondary importance, the great hairiness 

 of the whole exoskeleton (even exceeding that of the bristly 

 E chino somatinœ), the relatively large size of the head, the com- 

 plete fusion of the eleventh and twelfth abdominal segments 

 (pygidium and metapygidium), the small size of the sternites 



