12 Aracknida and Myriopoda 



Order Acari. 



The Acari or rnites are mostly of minute size, and their body 

 is usually unsegmented. There is a great diversity of structure in 

 this order, members belonging to different families often being 

 very dissimilar in general appearance. Perhaps the most 

 characteristic feature of the Acari is that they pass through a 

 six-legged larval stage. 



The Acari may be divided into eight principal divisions or 

 orders, which are as follows : — 



Sub-Obdees of Acaei. 



i. Vermiformia (Family — Demodicidae). 



2. Tetrapoda (Family — Eriophyidae). 



3. Astigmata (Families — Sarcoptidae, Tyroglyphidae, etc.). 



4. Cryptostigmata (Family — Oribatidae). 



5. Heterostigmata (Family — Tarsonemidae). 



6. Prostigmata (Families — Trombidiidae, Tetranychidae, Che- 



letidae, Bdellidae, Hydrachnidae, etc.). 



7. Mesostigmata (Families — Gamasidae, Spelaeorhynchidae, 



Holothyridae '?, Argasidae, and Ixodidae). 



8. Notostigmata (Family — Opilioacaridae). 



Acaei and Man. 



The species of Acari which are directly injurious to man are 

 not very numerous, the following being the most important : 

 the Eocky Mountain Fever Tick (Dcrmaccntor venustus) ; Orni- 

 tliodoros moubata, the tick transmitting human spirochaetosis in 

 tropical Africa ; the Japanese Harvest Bug, called Tsutsugamushi 

 (Microtrombidium akamushi), carrier of the Kedani or Eiver Fever 

 of Japan ; and the Itch-mite (Sarcoptcs scabici, var. hominis). A 

 number of species of minor importance are also recorded below. 



These species of Acari causing injury to man may be divided 

 into several different categories according to their habits : — 



1. Parasitic species. — First of all there are two minute mites 

 which are peculiar to man, viz., Dcmodex folliculorum (Fam. 

 Demodicidae) and Sarcoptes scabici (Fam. Sarcoptidae) ; it is 

 possible that the latter is only a variety of a species occurring on 

 several other animals as well as on man. Ornithodoros moubata 

 is another human parasite, man being the principal host of this 

 tick; and this is probably true also of 0. talaje, but a variety is 



