CHAPTER XVIII 
ARACHNIDA EMBOLOBRANCHIATA (CON TINUED)— ACARINA—HAR- 
VEST-BUGS—PARASITIC MITES——TICKS——SPINNING MITES— 
STRUCTURE—METAMORPHOSIS——CLASSIFICATION 
Order IX. Acarina (Acari, Acaridea). 
Arachnids with unsegmented, non - pediculated abdomen. 
Respiration by tracheae, or by the general surface of the body. 
Mouth parts suctorial, but frequently capable of biting or piercing. 
Metamorphosis always observable. 
THe Acarina or Mites are remarkable not so, much for the 
number of their species, which is very considerable, as for the 
vast multitude of individuals of the Order, which is far in excess 
of that of any other Arachnid group. This fact is correlated 
with their minute size. Very few Mites exceed half an inch 
in length, while very many are microscopic creatures, often 
measuring less than the hundredth of an inch. Taken all 
round, a millimetre may be considered a large size for a Mite. 
There is much variety of habit within the Order. All Mites 
live principally on fluid nutriment, but it may be obtained from 
living animals or plants or from decaying organic matter. Some 
are entirely parasitic upon plants or animals; others attach 
themselves to animals in their larval stage, but are free when 
adults; while others, again, live an entirely independent and 
predaceous life. 
The greater number of the Mites are too small to strike the eye. 
Some of them have, however, contrived to attract attention, in no 
very agreeable manner. Every one knows the Mite popularly called 
the “ Harvest-bug,” but to this day there is some uncertainty as to 
1 The single exception is Opi/ioacarus, see p. 473. 
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