413 



A. jacohsoni and A. esau are interesting from several points of 

 view. They prove above all the occurrence of speciñc and 

 sexual differences in internal organs apart from the reproductive 

 system, and render it certain that an examination of these organs 

 for systematic purposes would be fruitful. We know as yet very 

 little about the individual, seasonal, geographical, and specific 

 variation of the internal organs of insects ; insect-systematics 

 are still essentially a science of external features. 



Sexual difference in the shape of the stomach was not known 

 of Earwigs. However, only a few forms have been examined 

 anatomically, and it is therefore premature to say that Arixenia 

 is an exception among Dermaptera. 



A further point of interest is this, that the male and not 

 the female has the same form of stomach as the immature 

 Arixenia. The simplification of the stomach in the female, 

 however, may be a secondary acquisition due to the large de- 

 velopment of the ovaries in the gravid female. 



Reproductive System. 



As the specimens of Arixcnia esau described in 1909 were all 

 immature the reproductiv^e organs of the genus remained un- 

 known. W'c were naturally very interested to know whether this 

 anomalous Dermapteron exhibited any such striking character- 

 istics in these organs as for instance the viviparous Hemimerns, 

 or whether they were of one of the usual Earwig types. 



The organs of reproduction vary to a great extent in the 

 Dermaptera, and not only furnish reliable distinguishing char- 

 acters as regards species, but in many cases are also the safest 

 guides in establishing the relationship of the species and genera, 

 i.e. in drawing up a classification. Vekhoeff was the first 

 to make use of them for the grouping of the species and genera, 

 and Z.VCHER (191 1) adopted that method in his important work 

 on the Protodermaptera and other contributions to Drrmap- 

 terology. The reproductive organs of Arixenia are of an l'2ar- 

 wig type, but exhibit important peculiarities. 



The quantitatively chief part of the male reproductive system 

 of Arixenia is a large compact organ of copulation or penis, which 

 extends to the basal third of the abdomen and is curwd in 

 crook-shape at its proximal end (le.xt-lig. 24). The testicles are 



