PARASITES OF ANIMALS. 53 
peculiarities of their structure, habits, andmodes of reproduc- 
tion, as well as to their great practical importance with refer- 
ence to human health and property. 
The total number of species hitherto described, from all 
animals, is more than 2,000. Of these upwards of 100 species 
are found in domestic animals and man. 
The parasitic worms of man and domestic animals are nat- 
urally divided into four principal orders, which are character- 
ized by important anatomical and physiological peculiarities. 
I. Cestopes. (Tape-worms). 
This order includes the numerous kinds of tape-worms and 
their young, the “ measles,’ hydatids, and bladder-worms, 
found in more or less abundance in all classes of vertebrate 
animals, as well as in insects, mollusca, ete. These tape- 
worms helong to three very distinct familics and to numerous 
genera. About 250 species have been hitherto described. 
These worms in the sexually mature condition have a more 
or less enlarged roundish, oval, angular, or lobed head, desti- 
tute of a mouth, but provided with two or four suckers, or 
pits, and often with one or four proboscis-like organs, sur- 
rounded by hooks, by means of which they fasten themselves 
securely to the mucous membrane of the intestine of the 
animal in which they live. There is no intestine or other di- 
gestive system.. The head is followed by a series of many 
flattish joints or segments, those near the head being small 
and short, while those that are more distant are larger and 
usually oblong or squarish. These joints, as they mature, are 
spontancously detached and may enjoy a short independent 
existence, and are then called proglottides. Each joint con- 
tains distinct male and female reproductive organs, and 
matures a vast number of eggs, which are generally liberated 
‘reference more particularly to the internal parasites of man. Large 8vo, 480 
pages, with numerous figures and 21 plates. London, 1864. 
J. L. W. Thudichum. On the Parasitic Diseases of Quadrupeds used for food. 
In the Seventh Report of the medical officer of the Privy Council, p. 303. Lon- 
don, 1865. 
T. S. Cobbold. Tape-worms (Human Entozoa), their sources, nature, and treat- 
ment; 12mo, 83 pages, with figures. London, 1866. 
R. Leuckart, Die Menschlichen Parasiten, und die von ihnen herriihrenden 
Krankheiten. Two volumes, 8vo, with numerous figures. Leipzig and Heidel- 
berg, 1862 to 1868. Digitized by Microsoft® 
