ANATOMY AND PHYSIOLOGY. 183 
elaborate piece of mechanism. It is framed in two 
symmetrical halves, which are united in the middle 
line. Between the two segments, in the looser tissue, 
a passage is found for the poison duct, the oviduct, 
and the termination of the alimentary canal, arranged 
in this order. The poison duct lies lowest, just above 
the scabbard which, besides its other use, serves to 
bind the two segments of the bulb firmly together 
along their lower edge. On the upper edge of the 
bulb, and half encircling it, a kind of saddle is loosely 
applied. This is the seventh dorsal scale of the 
abdomen, the twelfth larvalsegment. Its real nature 
is obvious, from the spiracles and trachez which we 
can trace on it. In the male this saddle is not found 
here, but appears as an external dorsal scale, adding 
so much to the length of the abdomen in this sex. 
Just beneath this diminutive scale lies the end of 
the alimentary canal, with its vent-cover as already 
described. The orifice by which the alimentary canal 
opens externally is almost common to it and to the 
oviduct, as in birds; the two tubes being separated 
only byathin membrane. The edge of this membrane 
is marked by a tubercle from which a pair of palpi or 
feelers spring. These are not flexible and jointed 
like the palpi of the mouth, but straight, and covered 
on the outer side with fine hairs. When at rest they 
lie beneath the bulb, parallel to the sting, which lies 
between and below them, pointing the different way. 
But, as we press the abdomen and the bulb protrudes, 
they diverge from the sting and from each other. As 
the bulb revolves on its axis they point upwards, and 
the sting, ready to strike, points downwards. Their 
use may be conjectured, in the absence of direct 
