216 Trans. Acad. Sci. of St. Louts 
formerly protruding, are sunk in a eavity which is placed in 
communication with the pulmonary organ of respiration, which 
allows of a current of air continually renewed to bring odors to 
them.’’ ‘‘For my part, I believe that this homology is true. 
Then the antennary ganglion will become the olfactory bulb, 
its nerve terminations will be the numerous little olfactory 
nerves, the antennary nerve will become the tractus olfactorius 
and the antennary cerebral lobe will become the olfactory lobe.’ 
‘‘But the antennae of insects are an olfactory organ turned 
inside out, prominent in space and certainly very mobile. This 
certainly allows us to suppose that the sense of smell may be 
much more relational than ours, that the sensations thence de- 
rived give them ideas of space and direction which may be 
qualitively different from ours.’’ ‘‘In reality a sense of smell 
which admits of distinguishing space is a kind of sixth sense 
very difficult for us to describe. But all evidence points to the 
fact that insects with mobile antennae have such a sense. In 
this way the sense of smell directs them much better than mere 
perception of odors. This fact also explains how ants distin- 
guish the right side from the left side, the front from the back, 
by their sense of smell, and know when following a track or a 
trace, in what direction they are following it. Finally» pur- 
suant to the laws of association, it allows insects an olfactive 
memory of places such as relational sense alone posesses.”’ 
It is gratifying indeed to find that comparative anatomy thus 
gives us morphological substantiation for our findings in the 
field. Forel says, ‘‘A sense of smell which admits of distinguish- 
ing space is a kind of sixth sense very difficult for us to de- 
seribe.’’ It may be difficult in the case of the tiny creatures, 
ants, with which he worked, but a little careful imagining on 4 
— scale and comparing with other sense organs will make it 
ear. 
Among our own five senses, only three—sight, hearing and 
possibly smell—bring us information on distance and direction 
of distant objects; touch and taste have no part in this. Let 
us consider the simple mechanics of these three organs in our- 
selves. We receive visual impressions of an object by the turn- 
ing of the eye, the adjustment of the muscles, in that direction; 
we can estimate distances only by the muscular converging of 
