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Order 1 . Araneina, or True Spiders. 
Order 2. Pedipalpi , containing the scorpions, false scorpions and 
daddy long-legs. 
Order 3. Acarina. Containing the mites. 
The third order— Acarina —is the only one of these 
we shall have occasion to refer to. 
The Class Scolecida. or Entozoa is a somewhat heterogeneous group, 
containing several orders differing very widely from each other in 
characteristics and habits. These are usually given as follows : 
• 
Order 1 . Trematoda. Containing the flukes. 
Order 2. Cestoidea. Containing the tape-worms and bladder-worms. 
Order 3. Acanthocephala. Containing the spine-headed worms. 
Order 4. Nematoidea. Containing the thread-worms, hair-worms, etc. 
Two or three other orders, which are not parasitic, are included. 
This outline of the classification will suffice to give the reader an 
idea of the relative positions which the species we shall have occa¬ 
sion to refer to, occupy in this extensive sub-kingdom. These three, 
classes contain all the minute animals which can in any sense be 
called parasitic. For example, in the Insect class we find such para¬ 
sites as fleas, bed-bugs, lice, bot-flies, sheep-ticks, etc.; in addition to 
which there are many others, not true parasites, which direct their 
attacks more especially against man and domestic animals, as mos¬ 
quitoes, the Tabanidae , or horse-flies; the Simulidae , or black gnats, 
etc. 
In the spider class the principal enemies of man and beast are 
found among the mites and ticks, but these are counted by the legion, 
for almost every animal has its peculiar species. 
In the class embracing the intestinal worms we find whole groups 
of species which appear to have been formed for the exp t ess purpose 
of making the internal parts of mammals their special habitation, as 
they are unable to exist anywhere else. The stomach, the intestines, 
the -muscles, and even the brain and eyes have their peculiar species. 
It will be seen therefore that to investigate thoroughly the various 
parasites that infest our domestic animals, it is necessary to examine 
into each of the three classes of Articulates named, and to pass be¬ 
yond the boundary to which the work of the entomologist is usually 
confined. 
SHEEP PARASITES. 
This valuable and all-important domestic animal appears to be un¬ 
fortunate, in being attacked by more than the usual number of para¬ 
sites attacking the various, species of mammals. It numbers among its 
enemies species from all three of the classes named; and what is of 
still more importance, is the fact, that it suffers more severely from 
these attacks than any other domestic animal. 
