412 



of it, i.e. below it if the specimen is examined upside down, 

 we find the orifice of the oviduct. Farther back we find two 

 large genital sclerites, which we consider to be the eighth sternite. 

 The plates are strongly chitinised and hairy, being larger than 

 it is known of any other Dermapteron (text-fig. 23, st. 8). The 

 two sclerites border a median longitudinal groove, at the proximal 

 end of which the orifice of the receptaculum seminis is situated 

 (o.rs). The groove is membranous, but terminates anally in 

 a triangular, obtuse, horizontally flattened sclerite, which is a 

 solid piece of chitin and serves as a grip or clutch (clu) for the 

 male armature in copulation, as we shall describe farther on. 

 The proximal edge of the clutch is raised, and the anterior vertical 

 surface thus formed is concave, there being also a groove, a deep 

 one, behind this ridge ; sometimes the ridge is distinctly enlarged 

 backwards over this groove, the clutch appearing doubled up 

 horizontally. We have not found any gonapophyses. 



Respiratory and Nervous Systems. 



The adult and immature ^4 . jacohsoni agree with the immature 

 A. esan. The main chain consists of eleven ganglia, and there 

 are ten stigmata (cf. Jordan, 1909). 



Alimentary Canal. 



The main divisions of the alimentary canal observed in 

 Dermaptera generally are also found in Arixenia. Both sexes of 

 A. jacohsoni have the same very long and large oesophagus as 

 in A. esau, upon which follows the short proventricle. The 

 middle gut is widened at its commencement in both species into 

 a large sack extending towards the right side. While the posterior 

 portion of this stomach, however, is coiled up spirally in three 

 convolutions in A. esau, this is not the case in A. jacohsoni, 

 and we observe this noteworthy fact that in the immature 

 jacohsoni (one examined, sex not known) and in the males 

 (several examined) the stomach makes one and a half to two coils, 

 whereas in the female (two examined) there are no convolutions. 

 In this sex the middle gut and the small intestine form an elbow, 

 the small intestine being again elbowed a short distance from 

 its junction with the stomach. These difíerences in the shape 

 of the stomach between the sexes of A. jacohsoni and between 



