PHYTOPTUS OF THE BIRCH- KNOTS. 



85 



difference in form between tlie species of sucker-foot and the 

 neighbouring bristle appendages is clearly visible. In the act 

 of walking the terminal portions of the leg are pressed down 

 so as to be almost at right angles with the parts above, and 

 the sucker-foot may be seen with a small enlargement at the 

 extremity while free; when the leg is drawn forward in the 

 act of being raised the appendage may be seen curved 

 backwards as if still adherent, and then loosened and with- 

 drawn with a sudden jerk. 



Fig. 6 represents the PJujloptus much magnified, but still, 

 from the exceeding minuteness of the mite, gives only a 



Ii«.5 



Kq,6 



general idea of its structure. The chief peculiarity in the 

 appearance of this species, compared to the figures which I 

 have had the opportunity of examining, is in the greatest 

 width being immediately behind the insertion of the legs, 

 instead of further back, so that the somewhat sudden 

 tapering to the head gives it a more angular form. The 

 caudal extremity is distinctly lobed, and capable of being 

 curved downwards, and of free use as a caudal foot of 

 sufficient power for the gall-mite to raise itself on it 

 completely free of other support. On each side of this 

 caudal foot is a stout bristle, and at a short distance a 

 smaller pair is set on the upper part of the back. Three 

 other pairs are placed — one just behind the insertion of the 

 legs, the others at short distances from them along the sides 

 of the body. These hairs appear, excepting in the case of 

 the caudal bristles, to be frequently deciduous after death ; 



