PHYSOKEKMES ABIETIS. 133 



bifurcations of the branches or similar situations. These 

 forms are described below under a and /3 respectively. 



. Form more or less wedge-shaped, with the exposed 

 posterior portion broadly rounded outwards from the 

 comparatively flat ventral surface (PL LIX, figs. 2, 3) ; 

 anterior portion completely hidden between the bud- 

 scale and the branch, suddenly attenuated anteriorly, 

 and exactly fitting the inequalities of its resting-place. 



/3. Form more or less spheroid, with the ventral 

 surface slightly flattened and the cephalic extremity 

 suddenly attenuated. This form is comparatively rare 

 in this country. 



There are many forms intermediate between a and /3. 

 In some instances the cephalic extremity is suddenly 

 truncate or emarginate (PL LIX, fig. 4), but it is 

 usually much attenuated. On macerating the insects 

 in caustic potash, and observing them without pressure 

 (PL LVIII, figs. 4, 5), the cephalic extremity appears 

 more pointed than in the living insect, due, un- 

 doubtedly, to the swelling out of the irregularities of 

 the dermis, which in life bears the impressions of the 

 food-plant. Cornicles (PL LIX, figs. 5-5 b) at pos- 

 terior extremity shining black, hemispheric or elongate, 

 and sometimes double (fig. 5 &) ; there is a deep ventral 

 slit extending from the cornicles towards the cephalic 

 extremity, and on the dorsal surface are usually three 

 radiating grooves or depressions, the central or dorsal 

 groove being deepest, the outermost pair less pro- 

 nounced. Dorsal dermis (PL LVIII, fig. 6 a) with a 

 distinct pentagonal tesselation, and large derm-cells, 

 which are more numerous towards the posterior ex- 

 tremity, more particularly in the region of the cornicles 

 (fig. 6), where they are also much smaller and appear 

 to have long connecting tubes. Mentum (PL LVIII, 

 fig. 7) short, with several fine hairs at the apex ; 

 filaments, when expanded, rather long. Spiracles 

 (PL LVIII, fig. 9) somewhat trumpet-shaped, with a 

 long stem and a broadly dilated and circular flange. 

 Anal ring (PL LVIII, fig. 8) very small, and probably 



