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size of the glands, while heat increases it but hardly enough for one to 
dogmatise on the matter. 
Landois’ two remarks that the “ preparation of the scent glands is 
difficult ” and further on, “ it is.. .extremely small, so no one is at all 
surprised that up to the present it has been entirely overlooked,” are 
possibly due to the above noted fact about the size of the glands varying, 
a point which he does not mention. 
The two glands have each, as already said, a separate opening to 
the exterior, besides which they have an intercommunicating passage 
(Figs. 13 and 31). This runs across on the ventral surface, and in the 
middle line under the meta-thorax opens out to a large chamber in which 
lies what, for reasons to be given later, would seem to be an olfactory 
organ. 
It may be held as fairly certain that where individuals of any species 
have a characteristic odour, others of the tribe are able to recognise it. 
With many insects sensitiveness to this, especially in the case of the 
males at mating times, is so extreme as to be almost incredible, but the 
nature and even the place of the sensitive organ are often impossible to 
define. 
Bugs would appear to have a sense of smell, for according to A 
Manual of Entomology, by Hermann Burmeister (trans. W. E. Shuckard, 
H.E.S.), “ they are sensible to all kinds of odours : for example, citric 
acid, the sweat of horses, assafoetida, sulphur, etc., will drive them 
away for a time.” The writer cannot vouch for the foregoing, but on 
examining the ventral surface of a bug which has been mounted whole 
in balsam, there is found at the level of the coxae of the middle pair 
of legs, or perhaps a little lower, a somewhat peculiar organ. Although 
inside the body, it can quite easily be seen through the chitin, if the 
creature has been for a considerable time without a meal, and hence 
has become more or less transparent when so mounted. The shape is 
shown by the sketch (Fig. 29). At first sight the most noticeable 
feature is its “ dotted ” appearance. This is due to the organ being 
composed of club-shaped—or as Landois says, flask-shaped—ampullae 
imbedded head downwards in its substance, the handles of the clubs, 
which project shghtly above the surrounding surface, appearing like 
small buttons (Fig. 30). These ampullae, which are hollow, seem to 
be made of a very stiff material, possibly chitin, as in some microtome 
sections they have been hfted bodily from the surrounding tissue. Quite 
close to this organ, but rather anterior to it and more dorsal, is the 
thoracic ganglion which supplies it with nerves (Fig. 33). Comparing 
