ANATOMY AND PHYSIOLOGY. 135 
detected anything like the sounding comb of the 
humble-bee in the spiracles of any of the different 
kinds of wasps which I have examined. 
As we follow the course of the spiracle still further 
in, it takes the form of a narrow flattened tube. 
The point of interest is its junction with the trachea. 
On one side this is marked by the horny slip so often. 
alluded to, which is turned neatly round the flattened 
edges of the tube. From the opposite side a very 
delicate membrane projects into the canal to meet 
the slip. For about two-thirds of its length the edge 
of this membrane runs straight, but, at about one- 
third from the lower end of the stigma, the straight 
line is interrupted by the projection of the broad 
base of a flattened hook which rises from it. The 
point of the hook turns back and gives attachment 
to a few fine fibres, probably of the.nature of muscle. 
The base is continued by one edge, round the trachea, 
into the horny slip which keeps all these parts in 
position, while the other edge turns up, and is lost in 
the delicate fold of membrane. 
This is the respiratory larynx. In the larger, better 
developed thoracic spiracle, the use of the little hook, 
which appeared so enigmatical m the abdominal 
spiracles, is very obvious. The form of the external 
orifice of the stigma, and of the tube of the spiracle, 
differs much in the several kinds of Vespide, but 
the arrangement of the membrane, and of the hook 
regulating its tension, is uniformly the same in them 
‘all. And though not identical with, it is strictly 
analogous to the corresponding part of the more 
elaborate mechanism which Landois has described in 
the humble-bee. 
