130 Proceedings of the Royal Physical Society. 
Hf, ater nearly always walks in the same plane. as the surface on which 
it is moving, the tibiz alone being vertical. 
Sprracles. 
I have been able to locate only one pair of spiracles on the thoracic 
region, namely, on the metathorax just beside the wing attachment. 
Abdomen. (Figs. 8-11.) 
Tergites and Plewrites—These are visible dorsally. Hight segments are 
distinct. Except for the last four and for the spiracles of the first they call 
for no special mention. The spiracles of the first segment are very large, 
probably five times the size of the succeeding spiracles. On the tergites 
of segments 5, 6 and 7 paired membranous areas can be distinctly seen as 
semi-transparent oval patches. They are further distinguished by the 
nature of their bristles which are bifid and stouter than those of the 
general covering. Tergites 7 and 8 are of special interest, as they afford 
very definite secondary sexual characters. In the male beetle both of these 
segments are visible. In the female, tergite 7 covers tergite 8. The seventh 
tergite is further distinguished in the male as being the seat of a somewhat 
rudimentary stridulating organ. This is composed of two tiny processes on 
the posterior border of the tergite, and a stouter chitinous band extending 
across the tergite just anterior to these processes. In Hylastes ater, as. will 
be seen later, another secondary sex character occurs on the seventh 
abdominal sternite, but, in H. palliatus and H. cunicularius it is wanting, 
or not sufficiently marked to justify any reliance being placed on it. 
Accordingly, the secondary sex characters exhibited by the seventh and 
eighth tergites are of considerable interest. | 
Stermites—Seven of these can be distinguished. Sternites 1 and 2, 
however, are hidden by the coxe of the third pair of legs. They lie in the 
coxal cavities, and are represented by two membranous bands of chitin 
separated by a narrow linear fold. The remaining sternites, 3 to 6, call for 
no special mention. They are densely covered with fine bristles or hairs. 
Sternite 7 affords a valuable secondary sex character. In the male there 
lies in the middle of the sternite a distinct hollow fringed by a pubescent 
fovea which, despite wear and tear, is wonderfully constant. In the 
female, the 7th sternite is broader and deeper than in the male, and both 
depression and fovea are absent. I have found these characters of the 
greatest value in determining sex. The character of the male is mentioned 
by Fowler in his description of H. ater. Sternites 8 and-9 are probably 
represented by certain plates to be described later with the genitalia. 
