568 SCIENCE PROGRESS 



Five years ago we knew two internal parasites of the grouse 

 (endoparasites) 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 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 associated closely 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, how- 

 ever, 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. 



The interest of the insects and mites which live on the skin 

 of the bird is that these very likely form the second host of the 

 tape-worms, which undoubtedly do a certain amount of harm 

 to the lining of the alimentary canal. There are, for instance, 

 a couple of species of bird-lice, lively little creatures, which 

 take cover amongst the small feathers — which, by the way, 

 form their arid diet — like startled deer in the undergrowth 

 of a forest. Few grouse are free from these bird-lice, perhaps 

 hardly 10 per cent., and the number on each bird is to some 

 extent a measure of its ill-health. On a healthy grouse perhaps 

 but two or three are found. They are animals with stout and 

 powerful jaws, which they use to bite off the barbules of the 

 feather or the finer plumules which form their sole nutriment. 

 What fluid they obtain to moisten this somewhat dry nutri- 

 ment is not apparent, but the animals are active and by no 

 means so easy to catch as one at first thinks. They lay very 

 beautiful eggs attached in small groups to the base of the 

 after-plume of the feather or between it and the main shaft. 

 The young hatch out as miniatures of the parents and there 

 is no metamorphosis. The same species occurs on the Black 

 Grouse and upon the Willow, or Hazel Grouse. On a piner 

 these bird-lice increase enormously in number, and their 

 numbers to some extent serve as a measure of the gravity 

 of the disease. Both of these bird-lice cast their skin several 



