THE ECTOPARASITES OF THE RED GROUSE 361 



fluid dejecta from the caeca. The latter pass last, and often lie like a cap upon the 

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

 dropping. Mr Fryer first found them commonly at Fort Augustus in April. In 

 June they were not so common, owing perhaps to the rain, which washed the caecal 

 part of the droppings away. We examined a large number of the larvae both by 

 squashing them and cutting them into sections, but we found no trace of infection ; 

 in fact, here, in this most likely place, we again drew a blank. No specimen of 

 S. stercoraria or of its larvae has been found in the crop. This fly, which, as stated 

 above, we believe to be S. stercoraria, may eventually turn out to be a local variety. 



The larva of the fly has the usual maggot-like shape, tapering from behind 

 forward towards the mouth. Counting what appears to be the cephalic segment 

 but which in reality probably represents more than one segment, and which is 

 thus conveniently called the " pseudo-cephalon " l as one segment, there are 

 thirteen in all, the usual number for Dipterous larvae (Plate LVI., Fig. 2). 



The cuticle is thin, the maggots are white. They bear numerous small spines, 

 which are especially conspicuous in a ring around the anterior end of each segment. 

 These rings emphasise the segmentation of the larva. 



The " pseudo-cephalon " is pointed, and varies in outline according to the 

 extent of protrusion of the mouth and its sclerites. These sclerites are the most 

 conspicuous structures in the larvae ; jet-black, they stand out against the white 

 tissues of the maggot. There is a pair of hooks which apparently correspond 

 with the single median mandibular sclerite of Musca domestica.'* At the base of 

 each of these is a dentate sclerite, and the mandibular sclerite articulates behind 

 with the hypostomal sclerites. These latter are irregular longitudinal bars con- 

 nected by a slight transverse plate on the ventral side. In M. domestica the 

 salivary glands open into the pharynx just in front of the transverse piece. 

 Posteriorly the hypostomal sclerites are very closely articulated, or perhaps even 

 fused with the large lateral pharyngeal sclerite. This consists of a ventral plate, 

 continuous with two lateral plates which are deeply notched, and in the house-fly 

 the nerves and tracheae which supply the pharynx enter through this notch. The 

 two lateral plates are united anteriorly by a dorsal cross-piece. The whole of 

 these sclerites are being continually pushed forward and retracted by a complicated 

 series of muscles which have been carefully described in the case of M. domestica 

 by Dr C. Gordon Hewitt. 



1 L. F. Henneguy, " Les Insectes," Paris, 1904. 



2 0. Gordon Hewitt, Quarterly Journal of Microscopical Science, lii. p. 495, 1908. 



