Acari. 109 



Africa. In Europe they are known from Austria, France and Table-case 

 ^ . No. 25. 



Corsica. 



Drawings of Stylocellus sumatranus, to illustrate the structure 

 of the Anepignathi, are exhihited in Tahle-case 25. 



Order 9.— Acari (Mites and Ticks). 



These Arachnida, which show niany traces of degeneration, Table- 

 are most closely allied to the Opiliones. The cephalothorax and ^^3*^95.25 

 ahdomen are completely fused with one another, and the latter 

 region is usually without any trace of segmentation. The appen- 

 dages of the first pair vary in structure, heing sometimes chelate, 

 sometimes styliform, and often retractile heneath the fore horder 

 of the cephalothorax ; the basal segments of the appendages of 

 the second pair are fused beneath the mouth and project forwards 

 below, unitinglaterally with the " camarostome," or " rostrum," to 

 form a suctorial proboscis. 



The Acari are mostly of small, or even microscopic size. Some 

 live a free and predatory life ; others are parasitic for the whole or 

 part of their lives upon plants or animals. 



From an economic standpoint many of the Acari are of con- 

 siderable importance on account of the injury they inflict upon 

 plants ; and the Ticks are now known to be of great importance 

 in the transmission of certain diseases of man and domesticated 

 animals, more especially in tropical countries. 



They are divisible into the following sub-orders : — 



1. Notostigmata. 5. Aatigmata. 



2. Cryptostigiiiata. 6. Vermiformia. 



3. Metastigmafa. 7. Tctrapoda. 



4. Prostigmata, 



Sub-order I.— NOTOSTIGMATA. 



In the Notostigmata the abdomen consists' of ten segments, 

 which are defined by grooves in the integument, the four anterior 

 of them being furnished dorsally with paired tracheal stigmata. 

 To this sub-order belongs the single family Opilioacaridac. 



These mites have been found under stones in Algeria, Italy, 

 Arabia and South America. They are not parasitic. 



A drawing of Opilioacarus scgmcntatus is exhibited in Table- 

 case 25. 



