474 
[March 
minal ventral piece in Tenthredinidae and Uroceridae. {Ibid. p. 94, figs. 
Vlh and 15 h and p. 115, fig. 13 5.) In all species known to me belonging 
to A. I. the sheaths are capable of being concealed for their whole breadth 
in this “ caudal groove”; and it is only in one undescribed N. A. spe¬ 
cies belonging to A. I. (a unique specimen)* and also in C.gallse 
tinctorise, (Asia, another unique specimen) that I have found the 
sheaths projecting a little beyond the tip of the ^‘dorsal valve.” In all 
the rest which are known to me they do not, when reposing in the 
“caudal groove,” project at all from the “dorsal valve.” Each sheath 
is elongate-spoon-shaped, the convex side outwards, so that when they are 
compressed together in the “ caudal groove,” they form a hollow cyl¬ 
inder, rounded and closed at tip. In aciculata (12—15 specimens) 
they are curiously channelled on the inside, as if an impression in wax 
had been taken of the curved ovipositor with its fine hair-like tip (Fig. T. 
o) ; and there is a strong appearance, in many freshly relaxed specimens, 
of a membranous tubercle lying at the interior tip of the sheath in the 
curve corresponding to the hair-like tip of the ovipositor. In fact in 
the recently relaxed sheath its whole interior surface seems occupied 
by membrane, so as to present a plane surface with a groove sculptured 
in it of the exact shape of the ovipositor, while the very same sheath 
when dried will be concave inside with the groove indicated only 
by a shining stripe on an opaque surface. This tubercle may be, 
and perhaps is, the poison-secreting gland. On three or four oc¬ 
casions, on disengaging the ovipositor of aciculata from its sheaths, 
in the manner described above, I have found its recurved tip covered 
with a mass of whitish gummy matter soluble in water, and in two 
specimens, which happened to die with the ovipositor disengaged, I 
notice the very same thing.* Hence, and from the peculiar structure 
of the parts, so different from what we find in any other Spiculifera, I 
infer that the use of the “caudal groove” is to compress the sheaths of 
the ovipositor, so as to enable them to form a suitable gum-tight recep- 
table for the gummy matter, and that this gummy matter is the gall- 
producing poison, and probably secreted from the tip of the sheath 
itself. 
* This species turns out to be C. q. operator 0. S., as I have ascertained from 
specimens of that species sent me by Mr. Bassett.—March 14, 1864. 
