THE ECTOPARASITES OF THE RED GROUSE 351 



bristles. The male is readily distinguished from the female by the fact that in it 

 the third joint is produced into an inwardly directed process very like a thumb, 

 and this gives the antennae a biramous appearance (PI. liii., Fig. 1). 



The next three pairs of appendages are modified as mouth-parts, and in describing 

 them we propose to mention certain median structures also connected with the mouth. 



The most remarkable feature of the under surface of the head of a Goniodes is 

 a white cushiony area with the outline of a stout sausage, sometimes described as 

 the "upper lip " or " labrum." It is bounded anteriorly by a ridge of chitin. 

 This cushion is covered with a multitude of rugosities, giving it the appearance of 

 the skin of a dog-fish. There is always a more or less well-marked crease or groove 

 across the long axis of the cushion, and the part posterior to the crease is supported 

 by two longitudinal bars of chitin just as the double banners temperance reformers 

 carry in their processions are supported by the poles. 



If one be watching the living Goniodes lying on its back on a slide, this cushion 

 will be seen from time to time to swell up and scrape along the under surface of 

 the cover-slip. Then it subsides again, possibly being pulled back by the numerous 

 muscle-fibres which pass back from the anterior end of the head, and which appear 

 to be inserted into the inner surface of the cushion. Along the posterior edge of 

 the cushion is a small mobile membrane or lip which bears a moustache of eight 

 hairs, shorter in the centre, but increasing in length as one passes outward. This 

 lip is frequently drawn down over the tips of the mandibles. 



The only function one can suggest for the upper lip is that it acts as a scraping 

 organ, and it may be of use if the animal ever eats the epidermis of its host. 



III. The Mandibles. — These are by far the most powerful of the mouth-parts, 

 and are very strongly chitinised. The right and left mandibles are not exact 

 images of one another, as the tip of one always closes outside the 



. ° . ^ . ... Mandibles. 



tip of the other, and thus there is a slight difi'erentiation at the apex, 

 which is so strongly chitinised as to be almost black. Each mandible is somewhat 

 triangular in shape, the apex forming the tip. The articulation is very complex. 

 A very powerful muscle runs into the external posterior angle of each mandible, 

 the so-called condyle, and serves to bring it into biting contact with the other. 

 The sharp shearing-edge of the mandible is admirably adapted for cutting off the 

 barbules of the feathers which form the food of these biting-lice. 



IV. The First Pair of Maxilke. — -These are very difficult to see in the living 

 animal and are best observed when in movement. I agree with Grosse ' in 



' "Zeitschrift fur wissenschaftliche Zoologie," xlii. p. 537, 1885. 



