88 A. e. OUDEMANS, .MOTES ON ACAÄl. 



whilst I have always called this split the genital opening. 

 I may here explain my reasons. 



Firstly the protonympha of Tyroglyphidae shows already dis- ' 

 tinctly the pair of minute genital suckers a short distance before 

 the anal split. What Michael calls in the hypopus the anus 

 and I the genital opening, is in fact flanked, like in the deuto- 

 nympha, by two pairs of minute suckers. It is therefore more 

 probable that the split before the suckerplate is the genital 

 aperture and not the anal opening. But moreover I found in 

 all instances (and in nearly all my drawings of hypopi I have 

 represented it) a minute median opening in the sucker plate. 

 Michael has neither mentioned nor delineated this opening. I 

 have always considered this opening as the anal one. 



Of course we both do know well, that the so-called openings 

 are no openings at all, but indications of the places where 

 in the deutonympha the anal opening, and in the adults the 

 genital openings will break through. 



Secondly it is known, that most males of Tt/roglyphidae, 

 and I may say in general of Acaridae (= Sarcoptidae), have 

 their anus flanked by a pair of suckers, called anal suckers 

 or copulation suckers as they fasten or suck the female during 

 copulation. Now 1 have found that in Analgesidae, which are 

 very related to Tyroglypliidae [in spite of Michael's non uni- 

 ting the Tyroglyphidae (sensu Michaeli) with the remaining 

 Acaridae, or Sarcoptidae (sensu Michaeli)], the males often bear 

 their anus and suckers in a plate, which in many instances 

 exactly resembles the suckerplate of hypopi of Tyroglyphidae. 



Arnhem, September 1904. 



U Apiil 1908. Remarks. 1. The „Revision of the Cheletidae" of which on 

 pp. 79 and 8.5 is question, has since appeared in the Mémoires de la Socie'te' 

 Züologi(iue de France, Tome XIX, p. 36-144 (15 April 1907; and p. 145—218 

 (15 Octübei' 1907). — 2 That the present essay is published just now, three 

 years and a half after tlie closing, is wholly out of my fault. 



