116 MODERN CLASSIFICATION OF INSECTS. 
(hitherto regarded by all authors as the basal segment of the abdo- 
men) having a longitudinal impression down the middle. ‘The abdo- 
men is perfectly sessile, somewhat flattened in the males of Urocerus, 
but cylindrical in the females: in both sexes, the terminal segment is 
produced into a point; but it is much stronger, larger, and more 
horny in the females: in the latter, on the under side of the terminal 
Segment, is an impression which has been mistaken by Latreille for 
the anus. The construction and real nature of the instrument of ovi- 
position or borer of these insects has not been satisfactorily investi- 
gated; but which, from the peculiarity, structure, and habits of this 
osculant group of insects, is so necessary for affording proofs of the 
relation of the saw-flics with the other Hymenoptera. My jig. 72. 
13. represents a lateral view of the extremity of the abdomen of the 
female Urocerus juvencus, exhibiting, at @, one of the two minute 
pilose styles (hitherto unnoticed by any previous author), and which 
we have seen to exist in the Tenthredinide ; 6 represents the basal 
and 6 6 the terminal division of the outer horny flattened sheaths of 
the ovipositor, which in U. spectrum are nearly as long as the body. 
Between these sheaths, when at rest, lies the boring instrument c, 
a long horny piece which is nearly cylindrical and hollow, but in- 
closes in its lower cavity two horny spicule*, having a separate 
motion from that of the borer itself. F%g. 72. 16. represents a trans- 
verse section of this compound instrument; c being the borer, consist- 
ing of a horny cylinder, with lateral impressions c Xx, and channelled 
on the under side for the reception of the two spicule, ce ande. Lig. 
72. 14. represents asmall portion of the base of the under side of these 
instruments, showing the dilated root of the borer itself, c 0, and of 
the two spicule, c o: these spicule are slightly grooved at the base: 
one of them is here represented as propelled forwards by a muscle ; in 
which case, of course, its point would extend beyond the point of the 
borer, the spiculz and borer being of equal length ; at e is a groove 
in the oblique edge of the borer, which seems to receive a slight rib 
in the spicula. F%g. 15. represents the extremity of the borer c, part 
of it being broken off, in order to show the separation between it and 
the spicula ce, which is strongly toothed at the tip, or its under side ; 
and c x represents the Jateral impressions of the borer (as in fig. 16. 
c x ), forming a strong lateral serrature. On comparing these details 
treille incorrectly describes the terebra as ‘* bivalvulata.” (Genera Cr., 
p- 242.) 
