GALL BUTE. 213 



greatest width ; but its powers of elongation and contraction 

 make it difficult to give more than an approximate measure- 

 ment. From the insertion of the legs to the caudal foot the 

 Phytoptiis is marked with transverse strite of such minuteness 

 as to give about a hundred to the length of the body, these in 

 the early life of the Gall Mite being deeply corrugated; when 

 full grown the bands are marked with dots, about thirty-two 

 to the circumference of the mite, having a projection, when 

 seen against the Hght, as if possibly composed of a pencil of 

 short hairs. The legs, at full stretch, only extend about half 

 their length beyond the head, and when in motion the 

 difference in form between the 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 back- 

 wards as if still adherent, and then loosened and withdrawn 

 with a sudden jerk. 



The figure (p. 212) represents the Phijtoptus much magnified, 

 but stih, from the exceeding minuteness of the mite, gives 

 only a general idea of its structure. The caudal extremity 

 was somewhat 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 ; but whether from their absence, or from not 

 having a sufficiently powerful object-glass to discover them, 

 I was unable to see more than these five pairs of bristles on 

 or under the body. The corrugated furrows beneath, behind 

 the insertion of each pair of legs and of the head, with their 

 longitudinal lobes, and the movement of the mouth, as the 

 mite moved it on the surface of the slide, were clearly 

 discernible. 



The formation of the Witch-knots begins with a diseased 

 growth of the mite-infested bud, which is distinguishable by its 

 swelled, irregular, loosely-opened appearance, from the smooth 

 and pointed shape of the buds in healthy condition ; and pre- 

 sently, as shown in figure (p. 214), the attacked shoot is 

 thickly covered by the buds, which in healthy growth_ would 

 have been distributed at distances of some inches along it. As 



