Acari. 
109 
Africa. In Europe they are known from Austria, France and Table-case 
Corsica. No> 25, 
Drawings of Stylocellus sumatranus, to illustrate the structure 
of the Anepignathi, are exhibited in Table-case 25. 
Order 9. — Acari (Mites and Ticks). 
These Arachnida, which show many traces of degeneration, Table- 
are most closely allied to the Opiliones. The cephalothorax and ^g S 25 9g 
abdomen 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, being sometimes chelate, 
sometimes styliform, and often retractile beneath the fore border 
of the cephalothorax; the basal segments of the appendages of 
the second pair are fused beneath the mouth and project forwards 
below, uniting laterally 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. Astigmata. 
2. Cryptostigmata. 6. Vermiformia. 
3. Metastigmata. 7. Tetrapoda. 
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 Opilioacaridae. 
These mites have been found under stones in Algeria, Italy, 
Arabia and South America. They are not parasitic. 
A drawing of Opilioacarus segmentatus is exhibited in Table- 
case 25. 
