190 THE GROUSE IN HEALTH AND IN DISEASE 



were themselves markedly infested with an ectoparasite, a species of 

 mite. Here we refrain from quoting Dean Swift. The mite x belongs 

 to a sub-family all of which are parasitic upon insects ; these are re- 

 garded as harmless. Our specimens existed in considerable numbers, 

 clustered round the hinder end of the fly's abdomen on the ventral 

 surface, with their snouts or proboscides plunged into the body of the 

 insect. Many were laying eggs, and many cast-off cuticles were lying 

 around them. Eggs from which the larvae had escaped presented a 

 spindle-shaped outline ; others contained eggs in various stages of 

 differentiation ; others fully formed larvae. 



We have in no single case found a Grouse-fly in the crop of a Grouse, 

 nor have yet found any cestode larvae or cysts in the bodies of the flies 

 which we have cut into sections or dissected. 



(ii.) Fam. SCATOPHAGID.E SCATOMYZIDJE. Dung-flies. 



This family contains species many of which produce their larvae 

 alive and deposit them in the bodies of other insects, or on open sores, 

 or in organic material. The Grouse dung -fly cannot be looked upon 

 as an ectoparasite of the Grouse, but it lays its eggs in Grouse- 

 droppings, and its maggots live on and in these dejecta. The maggots 

 must therefore constantly be in close contact with and certainly eat 

 the eggs of the tapeworms which exist in such vast numbers in the 

 Grouse droppings; and hence it was thought a profitable object to 

 investigate for the second state of the cestode. It may be 

 recalled that each Grouse dropping consists of two parts (1) the 

 dejecta from the intestine strictly speaking, and (2) the more fluid 

 dejecta from the caeca. The latter pass last and lie like a cap 

 upon the former. The two lateral diverticula or pouches of the 

 bird's intestine known as the caeca are unusually large in the Grouse, 

 and in them the absorption of the digested food takes place. The 

 fly -maggots are only found in numbers in the " caecal " part of the 

 dropping. 



VI. Scatophaga stercoraria, Lin. The Grouse Dung-fly. 



The Grouse dung-fly is first found commonly in April. In June it 

 is not so common, owing perhaps to the rain having washed the 

 caecal part of the droppings away. A large number of the larvae have 

 been examined both by crushing them and by cutting them into 

 sections, but no trace of tapeworm cysts have been found, although 

 many weeks were spent in carefully searching through the tissues of this 

 and an allied species of dung-fly. 2 No specimen of either dung-fly or 

 of their larvae has been found in the crop of the Grouse (PI. xix. Fig. 3). 



1 Mr C. Warburton has kindly identified the mite as belonging to the genus 

 Canestrinia and probably to a new species. 



2 Scatophaga squatida, Meigen. 



