212 Sensory Perceptions in Ticks 
to drive them across the barriers. Accordingly the foregoing experi¬ 
ments were repeated in the dark but the results obtained were 
practically identical. 
From these results it would appear as if Argas persicus were only 
slightly susceptible to the effects of smells, but on employing different 
methods in the investigation of this subject very different results were 
obtained. 
(c) Experiments with vapours. 
Finally the following experiments were devised in which the 
complicating factors of touch and differences in temperature were 
eliminated. A definite number of ticks were placed on a level sheet of 
filter paper which was supported about three inches above the bench. 
By this means it was possible to introduce beneath the filter paper 
wide-mouthed bottles containing the various odoriferous substances. 
The ticks could therefore be exposed to the action of the vapours that 
rose through the filter paper without having to moisten the paper or 
place solid substances across their paths. The results were very definite 
and showed that Argas persicus undoubtedly possesses a well-developed 
sense of smell. 
The vapours of a large number of substances were tested and in 
practically every case the ticks proved susceptible to the odours. The 
following substances were tested :—ammonia, butyric acid, naphthalene, 
clove oil, phenol, and the faeces of a fowl. 
The ticks proved very susceptible to the effects of the vapours of 
ammonia and clove oil respectively. Immediately their front legs 
entered the region of the vapour the ticks precipitately retired and 
without exception avoided it. In the case of phenol, naphthalene, and 
butyric acid, respectively, the effects were slightly different. On 
entering the vapour the tick stopped and then stood still for a short 
time, waving its front legs in the air much in the same way that many 
insects move their antennae. Sometimes after one or two uncertain 
movements the ticks moved backwards away from the odorous region 
but in other cases they marched across it. 
In the case of all these substances the vapours are more or less 
irritating to any sensitive part of the body and therefore it was possible 
that these reactions did not indicate any sense of smell but were 
merely the result of the general irritating effects of these substances. 
Accordingly, an experiment was made employing the odour of fowl 
faeces which could not possess any general irritant properties. The 
