(dr. a. C. OtJDEMANS). NOTES ON ACARI. 95 



are still, provided with chelate mandibles. Yet a few primitive char- 

 acters have persisted, e. g. the situatien of the genital openings 

 behind the 4th pair of legs; an indication of segmentation in a 

 few members; etc. 



Berlese has proposed a third group, thai of the Cri/pstostigmata. 

 This group must fall. The three families of Oribatidae, Nicoletiellidae 

 and Acaridae, as to me, are not to be united. 



Their mutual relation and that with other already mentioned 

 families is far from being settled ; that of Orlbatldae with Acaridae 

 at least problematic. The Orihatidae oftenest have tracheae, and 

 even 4 pair of them, with 4 pair of stigmata, which, however, 

 are invisible, being situated in the thin connective membrane 

 between the body and the first free joint of 1 he legs. But these tracheae 

 are e.xtremely thin tubes, without any indication of a spiral chiti- 

 nous thread. Probably they have originated undependently from 

 the primitive tracheal system of the Arachnoidea, as a necessary 

 consequence of the enormous chitinous cuirass of the Orihatidae. 

 (It is obvious that weak Orihatidae miss the tracheae, and these 

 I consider as the oldest forms; see below.). The Nicoletiellidae {1) 

 and Acaridae are destitute of tracheae and stigmata; therefore one 

 should be inclined to place them in Kramer's group oî Atracheata, 

 or in Berlese's Astigmata. But I positively reject these groups, 

 because they are no natural ones; because they do not contain 

 two families, which are related. The absence of stigmata or tracheae 

 does not prove any relation; it is a result of convergency; the 

 Halacaridae, Demodicidae, Eriophyiiae, a few Hj/drarac/midae, the i of 

 the Tarsonemidae and a few Orihatidae too miss the tracheae ! 



Berlese's Astigmata contains the Demodicidae and EriojiJij/idae. 

 Now Demodicidae are parasites in the glandulae sebaceae of 

 mammals, and therefore probably descended from Sarcoptidae ; whilst 

 the 4-legged Eriophyidae inhabit galls , or are free living creat- 

 ures on the under-side of leaves, so that they probably have 

 plant-inhabiting Acari (e. g. Tetronychus e tutti quanti) as proge- 

 nitores. Summa summarum I admit the following classification: 



Tijdschr. v. Unioni. XL VI. 7 



