THE WEB OF LIFE 303 



harbours sixteen different species of flukes. Omnivorous 

 animals in particular are peculiarly liable to become hosts 

 of alimentary parasites. It is well known that oaks are 

 used as hosts by many different kinds of gall-flies. In 

 Europe, Quercus fedunculata harbours no fewer than ninety- 

 nine different kinds of gall-flies, Q. pubescens seventy-nine, 

 and Q. sessiliflora ninety-six. 



Grouse Disease. — Writing in 1911 on Grouse Disease, 

 Dr. Arthur Shipley said : 



' Five years ago we knew two internal parasites (endo- 

 parasites) and two or three parasites which live outside the 

 skin (ectoparasites). At the present time we know that 

 grouse, like other animals, have a considerable fauna living 

 both in and on them. They are, in fact, not only birds, but 

 in a small way aviating Zoological Gardens. The scientific 

 members of the Grouse Disease Inquiry have recorded eight 

 different species of insect or mite living either amongst 

 the feathers or on the skin of the bird or in other ways closely 

 associated with the grouse, and no fewer than fifteen animal 

 parasites living in the blood, the alimentary canal, the lungs, 

 or other organs. Some of these are negligible. They 

 either exist in too small numbers or infest but a very small 

 percentage of the birds ; others, however, are found in 

 about 95 per cent, of the cases investigated, and two 

 at least are associated with grave disorders which often 

 terminate in death '. 



One of these is a Nematode worm (Trichostrongyhis 

 pergracilis), of which there may be 10,000 in one grouse, 

 about equally divided between the two intestinal caeca, 

 and a microscopic Protozoon, Eimeria (Coccidium) avium, 

 which Uves in coimtless numbers in the dehcate lining 

 membrane of the food canal in young grouse. 



