426 THE DISEASES AND DISOEDEKS OF THE OX. 



it may be on a cold winter's night, when the snowstorm rages 

 around them — reflect the greatest honour on that hardy and 

 honest class of men. 



SECTION IV.— PARASITISM, 



THE WARBLE-FLY AND ITS LARVA; THE GAD-FLY 

 OF THE OX. 



The subject which we have chosen for this section is one of 

 great importance, even so far as its bearing upon the ox is con- 

 cerned, and manifestly much more is it of primary moment when 

 considered generally and in regard to its far-reaching issues 

 among the various races of mankind. The phenomena of 

 parasitism most intimately affect all ideas as to the evolu- 

 tion of, and the various connections existing between, the 

 innumerable living animals and plants which we find around us 

 in this wondrously constituted world of ours. 



Many writers, for convenience' sake, draw a great distinction 

 between those parasites which live on the external surfaces of 

 other animals and those which live within their bodies. We 

 do not think that this classification of animal parasites into the 

 ectozoa and the entozoa is of any real value, just as we do not 

 hold that a similar division of vegetable parasites into those 

 which adhere to the surface of other animals or plants, and 

 those which live within animals, would be anything but a most 

 misleading and artificial arrangement. 



In our remarks we shall not have time to do more than just 

 touch upon the outlines of our subject, and hence we shall say 

 but very little about the classification of parasites. 



Viewed from a broad aspect, parasitism furnishes an example 

 of those numerous kinds of antagonism with which the whole 

 world of life is so painfully replete throughout its numerous 

 and complicated ramifications. It is one of those groups of 

 strange and closely-allied facts with which observers of natural 

 history are very familiar. In common with all other living 

 creatures, man himself is liable to the insidious and often fatal 

 attacks of creatures quite insignificant, except in so far as their 

 powers for mischief are concerned ; and in this way, even when 



