ANIMALS WHICH LIVE ON OR WITHIN GROUSE 183 



blood of the Grouse, at any rate it is so constantly associated 

 with that bird that it seems to merit a place here. 



At first sight the attention paid to the Ectoparasites, or 

 animals which live outside the Grouse, mostly among the 

 feathers, may seem superfluous, but the study was rendered 

 necessary by the probability of establishing a connexion between 

 these Ectoparasites and the more important internal parasites. 

 Most of the internal parasites and all the tapeworms pass 

 through a second host. For example, the tapeworms which 

 live in the alimentary canal of the Grouse pass their younger 

 or larval stages in the body of some lower animal. This lower 

 animal, presumably an insect or a snail or a spider, must be 

 eaten and digested by a Grouse, and the larval tapeworm must 

 be thus set free before it can grow up into the adult tapeworm 

 which we find in the intestine of the Grouse. In searching for 

 this second host it was natural to begin with the Ectoparasites, 

 which one would imagine were continually being snapped up 

 by the bird. We have, however, up till now completely failed 

 to find any tapeworm larvae in the Grouse-fly or in the numerous 

 " biting - lice " or " bird - lice " l which abound on the skin 

 and amongst the feathers of the Grouse ; and what is still 

 more significant and still more remarkable, we have, in the 

 hundreds of crop contents which we have examined, never 

 found one of these insects amongst the Grouse's food. 



During the course of the recent investigations many ana- 

 tomical and morphological notes have been made which, though 

 interesting to the zoologist, have no direct bearing on disease in 

 Grouse, these have been published in another place. 2 Here, it is 

 proposed to give as complete a list as possible of all the animals 

 which infest the Grouse, but only to discuss at length such facts 

 as Jiave a direct though perhaps at times a distant bearing 

 on disease in Grouse. For there is no doubt that the worms 

 and unicellular animals (Protozoa) which live in various regions 



1 These form the group of insects called the Mallophaga, which is allied to the 

 Anoplura or true lice of man and other mammals. 



2 Proceedings of the Zoological Society of London, 1909, pp. 309, 335, 351, 363. 

 11 The Grouse in Health and in Disease," First Edition, pp, 348ff. 



