x INTRODUCTION. 



or enquiring turn of mind believe in many of the 

 complicated life-histories of the unbidden guests that 

 attack our farm-animals and ourselves. There are 

 many who look upon the marvellous and complicated 

 changes of some of the parasitic worms as mere 

 ' fairy tales ; ' but doubtless the hand of time will 

 obliterate this bigotry. 



In Poultry the parasites have not such a com- 

 plicated metamorphosis as we see in many that 

 attack other farm-stock, unless it be amongst some 

 of the innumerable Tapeworms that are found in 

 the intestines of the Common Fowl ; for most 

 Cestode worms have two distinct hosts during their 

 development — one in which the curious i cystic ' 

 or ' bladder-worm ' stage is found ; another in 

 which the adult sexual Tapeworm takes up its 

 intestinal abode. 



There are both Vegetable and Animal Parasites 

 upon warm-blooded animals, although the former 

 are few compared with the vast army of animal 

 1 guests/ The vegetable enemies are of extremely 

 low form — minute fungi, which nevertheless often 

 cause very obnoxious parasitic infection, notably 

 the human ' Ringworm,' which is not due to a worm 

 at all, but to a microscopic fungus, the Trichophyton, 

 which also affects animals and from which we can 

 take the disease. 



