402 



genus. The head-capsule has the more or less cordiform shape 

 generally found in Dermaptera, but is unusually short and 

 broad, and proportionately much larger than in true Earwigs. 

 It is shorter in jacohsoni than in esau on account of the anterior 

 or clipeal portion being somewhat reduced in a longitudinal 

 direction. For this reason the suture separating the labrum 

 from the head is nearer the antennae in jacohsoni than in esau. 

 The sutures which separate the clipeus from the irons ( =epi- 

 cranium) and the latter from the occiput (= protocranium) are 

 but slightly marked in Arixenia, being particularly indistinct 

 in jacohsoni, and in both species much less in evidence than in 

 many true Earwigs. The posterior angles of the head bulge out 

 considerably, the cavity thus formed serving for the accommo- 

 dation of manducatory muscles. The grooves on the occiput, 

 which indicate externally the points where the upper posterior 

 processes of the endoskeleton (= tentorium) are fastened to the 

 capsule, are well indicated in both species. Such a large develop- 

 ment of the frontal region and the mouth-parts is unknown 

 among true Earwigs. 



The eye is rather smaller in A. jacohsoni than in A. esau 

 and further differs in shape, being elliptical in esau and slightly 

 but distinctly reniform in jacohsoni. The number of facets is 

 eighty odd in the former and about seventy in the latter, being 

 in both species very much smaller than in any known true Ear- 

 wig. The reduction is accounted for by the habits of the 

 insects, cave-dwellers generally having atrophied or reduced eyes. 



The segments of the antenna increase in number during 

 the metamorphosis from eight to thirteen in the larval stages, 

 and fourteen in the imago, which is the usual type of develop- 

 ment in Earwigs, the increase taking place by a division of the 

 third segment. The first segment is essentially shorter than in 

 A. esau, being cylindrical and practically straight in jacohsoni 

 and more distinctly curved in esau. The antenna of jacohsoni 

 has free play forward and backward, whereas the first segment 

 of esau cannot be directed straight forward— at least so it 

 appears from the alcohol specimens. Besides the patches of 

 sensory pits observed on each segment of the antenna of esau 

 with the exception of the two proximal ones (and also more 

 or less developed in the same way in true Earwigs), the segments 



