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Sensory Perceptions in Ticks 
We have mainly worked with the fowl tick, Argas pei'sicus {OVen, 
1818), as owing to the kindness respectively of Prof. E. Marchoux, 
Institut Pasteur, Paris, and Dr A. Balfour, Khartoum, a plentiful supply 
of this material was placed at our disposal. Moreover, this tick lends 
itself for experimental purposes more readily than most other species 
owing to the ease with which it may be reared and the rapidity of its 
feeding. We have, however, also experimented with Ornithodorus 
moubata (Murray, 1877) and Hyalomrna aegyptiwn (Linn.) which were 
received by Prof. Nuttall from Africa. 
Reactions to light. 
It is well known that the majority of the Argasidae walk away 
from light and appear to search out dark corners in which to hide 
themselves. Lahille describes Boophilus as being strongly negatively 
phototropic and gives a series of diagrams showing the paths taken 
respectively by each of a series of adult ticks. These diagrams, 
however, whilst demonstrating that the ticks on the whole walk 
away from the light, thus suggesting negative phototropism, also show 
that the ticks deviate considerably from the straight direction, and make 
one hesitate in using the term phototropism. It is far more probable 
that the reaction to light is a combination of negative phototropism 
and a perception of any difference in the intensity of the illumination, 
and this view is in accordance with the results which we have obtained 
in the following experiments with Argas persicus. 
1. Phototropism, employing daylight. 
In all cases the reaction of the ticks to direct daylight was tested in 
the following manner. A large white sheet of paper was placed in 
front of a window and a line was ruled across it, at right angles 
to the direction of the rays of light. Twenty of the ticks to be 
examined were arranged along this line and allowed to walk freely in 
any direction. The results were as follows:— 
(a) 30 unfed larvae. In this case all walked away from the 
light. 
{h) 20 fed larvae. All negatively phototi’opic. 
(c) 20 unfed first-stage nymphs negatively phototropic. 
id) 20 fed 
(e) 20 adults. In this case although every tick walked off the 
edge of the paper at a point behind the line from which they started, 
