454 THE DISEASES AND DISORDERS OF THE OX. 



stood by those who are directly concerned in the appreciation 

 of its revelations." The tendency to change the place of abode 

 is one which is especially curious in its manifestations, and it 

 may be said that the study of parasitic worms opens up to our 

 view the very strangest facts of which the human mind can take 

 cognizance. Man himself, in spite of his unique position as 

 the highest of the creatures of this world, is liable to be the 

 host of a great variety of parasites, and there are certain species 

 for whose propagation the existence of human beings is 

 apparently an indispensable condition. 



This is by no means a pleasing reflection, though it is to be 

 remembered that we can by cleanliness and care in large measure 

 obviate the dangers we incur. It has been very truly said that 

 the amount of suffering which results from the presence of para- 

 sites within the interior of human beings bears a strict relation 

 to the degree of barbarism shown in the choice of food and 

 drink, and in the manner of eating and drinking. 



The best known, and from many pioints of view most important, 

 of the animal parasites which live within the bodies of other 

 animals are known as *' worms," and include round-worms, tape- 

 worms, flukes, and many others. Those parasites which are 

 known as *' hots " represent the larval stages of various species 

 of gad-fly, and belong to the (Estridae, a rather numerous family 

 of the class Insecta, ** Bots " infest the stomachs of horses, 

 and there is one called the Gastropliilus rhinocerotitis, which is 

 found in the stomachs of rhinoceroses both in India and 

 Africa. 



With regard to the entozoa generally, we may point out that 

 they may belong to any one of the following six groups, viz. '. 

 Trematoda or flukes, Cestoda or tape-worms, Nematoda or round 

 worms, Acanthocephala or thorn-headed worms, Arachnida, 

 and, finally, Insecta. 



We now proceed to consider some diff'erent groups of para- 

 sites. The Trematoda, or flukes^ comprise six distinct families. 

 They have their bodies provided with little holes or perforations 

 called suckers, and the word fluke itself is of Saxon origin, and 

 signifies anything flat. However, though some flukes, including 

 the common liver-fluke, are flat, the members of many species of 

 the order may be oval or even as round as a marble^ or bi-convex 

 or even filiform, while some may be so elongated as to resemble 



