INTERNAL ANATOMY. 91 



forming a pointed bow, the free ends of which are 

 connected with the ventral surface and turn backward 

 during the coitus. 



Nalepa says that the supporting sclerite of T. siro is 

 boat- shaped, and that the bulbous proximal end of the 

 penis fills its hollow.* He also says that in Garpoglyphus 

 anonymus the supporting sclerite is azygous,f and is 

 not fixed to the external cuticle ; it is a half-oval plate 

 the strong chitinized edge of which bends inward and 

 projects forward in a hook to which the retractor 

 muscles of the penis are attached. 



The Genital Suckers. The organs which are known 

 by this name ; and which are usually, but not invariably, 

 present in both sexes when they are present in either ; 

 have been the subject of much difference of opinion 

 amongst acarologists as to whether they are really 

 suckers. They are certainly in some way connected 

 with the external genital organs, i. e. the penis and the 

 vulva, but not with the bursa copulatrix ; they have a 

 sucker-like appearance, and in the male are undoubtedly 

 exerted at the time of coition ; this is however the 

 result partly, if not entirely, of the protrusion and 

 exertion of the penis ; on the other hand, there is not 

 any reason to suppose that those of the female are 

 exerted at that time. The organs are found in most 

 families of the Acarina, but the extent of their develop- 

 ment and the complication of structure varies greatly 

 in different families. In the Tyroglyphidge the so- 

 called genital suckers usually exist in both sexes ; but 

 in Hericia they are absent from both sexes, and in 

 Trichotarsus they exist only in the female. In the" 

 Tyroglyphidse and Sarcoptidse the organs, although 

 usually present, are in the simplest form ; there are two 

 on each side of the genital aperture lying in a pocket 

 formed by a fold, or double fold, of the cuticle. Nalepa, 

 who investigated them in Tyroglyphus longior, considered 



* ' Abth. I,' p. 215. 

 t ' Abth. II,' p. 134. 



