PARASITES OP 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. CESTODES. (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, etc. These tape- 

 worms belong to three very distinct families 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 lobedhead, 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 

 spontaneously 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 herrahrenden 

 Krankhciten. Two volumes, 8vo, with numerous figures. Leipzig and Heidel- 

 berg, 1862 to 1868. 



