ANATOMY AND PHYSIOLOGY. 173 
various forms which this last assumes that the 
specific distinctive characters are found. By this 
means the distinction between V. germanica and V. vul- 
garis, which the external markings of the two species 
often fail to give, has been established.* This organ 
consists of a horny case which occupies the end of 
the abdomen. It is formed of two valves opening 
along the middle line with a horizontal expanding 
movement very like that of the bivalve specula 
which Surgeons use for examining internal organs. 
The groove below is accommodated to the central 
spiné; while the upper one receives the rectum. The 
form of the vent-cover is adapted to the sex of 
the insect. Instead of a scale being laid half-round 
the bowel, the bowel pierces the scale obliquely, and 
the same end is accomplished by, if possible, a still 
more simple mechanism than has been described 
in the female. ‘The outer pair of valves end by 
a sharp, and more or less recurved point, which in 
Odynerus projects considerably beyond the end of 
the abdomen. Within, connected with the outer 
valves, lie a smaller pair of horny valves, which end, 
not in a hook, but in a filament whichis clothed with 
fine hairs. These filaments lie parallel to each other 
and to the intromittent organ which is placed just 
beneath them. They re-appear in the caudal palpi 
of the female in a larger and more distinct form. 
The end of the intromittent organ comes fully into 
view on their removal. Spoon-shaped in V. vulgaris, 
bifid in V. germanica, the various forms which it | 
assumes in different species are easy of recognition 
* Smith’s ‘ Catalogue of British Fossorial Hymenoptera,’ &. 1858. 
Plate V, Figs. 20 and 21. 
