E. Hindle and Gr. Merriman 
213 
effects were most marked. The ticks stopped suddenly on entering the 
region of the odour and, after waving their front legs, quickly retreated. 
Having proved the existence of a sense of smell in this species of 
tick we then proceeded to determine in which part of the body it was 
localised. Following the experiments of Lahille and Miss Jordan Lloyd 
and also from the peculiar manner in which the ticks moved their front 
pair of legs on entering a vapour, there was no hesitation in selecting 
Haller’s organ as the probable seat of the olfactory sense and experi¬ 
ments were made accordingly. 
II. Experiments on ticks without Haller s organ. 
In order to make certain that this organ was removed, the simple 
method of amputating the terminal joints of the first pair of legs was 
adopted. The tick very quickly recovers from the operation but when¬ 
ever possible the amputation was performed the day before the animal 
was required for experiment. The method of occluding the Haller’s organs 
by means of various substances was not employed, as with this method 
it is never certain that the organ is entirely covered and thus rendered 
functionless. 
As the experiments with odoriferous liquids and solids had given 
such indefinite results, they were not repeated in the present series of 
experiments but we proceeded directly to ascertain how these ticks 
without Haller’s organ reacted to vapours. Accordingly the last series 
of experiments was repeated, employing ammonia, clove oil, and fowl 
faeces respectively, the three substances which had produced the most 
marked effect on the normal ticks. The results were very striking. In 
the case of ammonia the mutilated ticks seemed unaware of its presence 
until they were in the middle of the region of vapour; even here they 
only seemed to be just aware of its presence in spite of the fact that the 
smell of ammonia was very powerful, there being a jar of strong liquid 
ammonia immediately underneath the filter paper. When clove oil 
was substituted for ammonia the ticks appeared unaffected by it, 
although some effects might have been expected as in the case of 
ammonia, because of its irritant properties. In the case of the fowl 
faeces all the ticks walked through the odorous region without any 
hesitation. 
The foregoing experiments prove that Argas persicus possesses a 
definite olfactoiy sense, which is situated in Haller’s organ. 
