GROUSE DISEASE 57i 



activity must depend on our knowledge of their life-history, 

 hence the stress which has been laid on the external parasites 

 which may function as the second or larval host of some of them. 



At the time the present Inquiry commenced to inquire there 

 were but two worms described as being in the alimentary canal 

 of the grouse — the large tape-worm which lives in the small 

 intestine all the year round, known to every sportsman, and 

 a slender thread-worm which inhabits the paired caeca or blind- 

 guts, which are unusually large in the grouse and play a very 

 important part in its digestion. The latter worm under certain 

 conditions, and when present in considerable numbers, is 

 associated with one of the two diseases which have especially 

 attracted the attention of the Inquiry. 



Davainea urogalli (Modeer). — Of the three tape-worms that 

 are found in the grouse, this species is by far the largest and 

 by far the most common. It exhibits little seasonal variation 

 and is found in considerable numbers all the year round. The 

 birds become infected at an early age. 



D. urogalli is normally found in the small intestine, though 

 sometimes parts of it are found in other portions of the ali- 

 mentary canal. As a rule, three or four individuals are met 

 with. At other times, especially in weakly birds, there are 

 dozens and these fill up the lumen of the intestine to such 

 an extent that it is difficult to see how food can pass along. 



D. urogalli, like most cestodes, produces a very large number 

 of eggs at any one time. It may be, at a rough estimate, at 

 least 100,000 but this figure is no measure of the reproductivity 

 of the cestode, because as fast as new segments break off at 

 one end new ones are formed just behind the head and the 

 animal goes on producing new segments very much in the same 

 way as a recurring decimal reproduces ciphers. Hence the 

 eggs of this cestode must be scattered in countless millions 

 all over the grouse moors. The}' are probably eaten by some 

 insect or land mollusc and in the body of these invertebrates 

 change into the cysticercus or larval stage. 



The popular notion that grouse do not eat animal food is 

 entirely wrong. For the first three weeks of the bird's life 

 the greater part of its diet consists of insects or arachnids and 

 from the crop of the first grouse I ever dissected I took six 

 saw-fly larvae, eight caterpillars of a Geometrid moth, one 

 caterpillar of a smaller moth, two small Tineid moth and a 



