The Male Genital Anaature of tin Dermaptera. 



417 



are the preputial sacs, or penis proper. There are a pair of these 

 in the Protodermaptera, though one is aborted in the Hemiimrina, 

 Arixenia and Karsehiclliiuv, but only one in the higher Eudermap- 

 tera. Within the preputial sacs is a tube called the virga, a 

 portion of the ejaculatory duct, which also offers a great diversity 

 of form and affords highly valuable characters. The virga may be 

 a simple tube, a mere extension of the ejaculatory duct ; in many 

 groups it is protected, especially near the base, by a fine spiral 

 binding, the " spiralversteifung " of Zacher, which is especially 

 noticeable in the inflated basal 

 vesicle seen in many groups. In 

 the Labidurinte, the virga is un- 

 dulated and serpentine ; the length 

 of the virga and form and armature 

 of the basal vesicle offers useful 

 specific characters, especially in 

 the Forficulvhv. The preputial 

 sac is frequently furnished with 

 chitinous plates or disks, and some- 

 times with a series of minute teeth. 

 In order to detect the latter, and 

 generally to examine the virga, it is 

 necessary to use a high power of 

 magnification, and often a careful 

 manipulation of light, as the virga 

 and the armature of the preputial 

 sacs are often faint and difficult to 

 extinguish. 



While, I think, everyone will 

 agree that Zacher overrated the 

 value of the genitalia, yet they 

 undoubtedly afford extremely use- 

 ful generic and specific characters. 

 In the lower earwigs we find a 

 considerable complexity of armature, 



simpler and simpler till we meet a general uniformity in the 

 highest groups. 



Probably their study will enable us to define species in such a 

 group as the Echinosomatinas, where mere differences of colour are 

 still used as specific characters ; and in the Psalidse, where there is 

 a great uniformity of external features ; the study of these organs 

 may enable us to demarcate the genera. 



As far as we can yet see, it looks as though the genera based 

 upon these characters may coincide with geographical groups. In 

 the Pygidicranidse, we find the Ethiopian genus Dkrana sharply 

 distinguished by the structure of the genitalia from its Neotropical, 

 Oriental, and Australian relatives — that is to say, the type of 



Fig. 56. — Eudermapterous 

 Type. 



a. Metaparameres. 



b. Proparameres. c. Hinge. 

 Preputial sac in erection. 

 Virga (with spiral structure). 

 Reniform or basal vesicle of 



virga. 

 Ejacu atory duct. 

 Simple virga. 

 j. Protruded end of virga. 

 k. Denticulations. 

 l. Chitinous armature of basal 

 or reniform vesicle. 



E. 

 F. 

 G. 



H. 

 I. 



the 



genitalia becoming 



