CHAPTER VII 



ANIMAL PARASITES 



I MIGHT apologise to my readers for introducing 

 such a subject ; but science has no blushes. The 

 term ''parasite," as I intend it here, includes only 

 those minute animals that infest other animals, 

 either internally or externally. Most of them are 

 nourished at the expense of their hosts, but some, 

 such as the parasites of the pike and the pigeon, 

 appear to confer a benefit upon them. In com- 

 mencing we have to recognise one prominent fact. 

 All living animals, great or small, are pestered 

 more or less by other animals specially adapted to 

 prey upon them. Man himself has more than 

 fifty distinct species of known parasites. The dog 

 and the ox furnish about two dozen species each ; 

 while the frog proceeds upon his watery w.iy, 

 accompanied by at least twenty kinds of these 

 uninvited visitors. Even the slug, whose viscid 

 secretions might be regarded as an effective barrier 

 to all such trespassers, has its own special parasite, 

 which plunges through the exudations of its host 



