208 
Sensory Perceptions in Ticks 
In this case two conflicting influences are at work. First, the 
action of the horizontal rays tending to drive the tick in a direction 
away from the source of light owing to the negative phototropism. 
Secondly, the difference in the intensity of the illumination after the 
line XY, the perception of which is so strongly developed in these 
animals, that when they entered the region of brighter illumination, 
although the latter by reason of its vertical direction could not have 
any phototropic effect, the ticks retreated from this area, preferring to 
remain in the Ibss brightly illuminated part of the paper even in 
opposition to their negative phototropism. 
Reactions to gravity. 
The reactions of A. 2 '>ersicus to the action of gravity are not well 
marked. The experiments were conducted in a dark room in order to 
avoid the influence of light. Several of the ticks to be examined were 
placed in the middle of a large sheet of paper and the latter was then 
supported vertically. In all stages it was found that roughly speaking 
the unfed ticks merely scattered in all directions whilst the fed ones 
practically always walked towards the bottom of the paper. This effect 
was most marked in the case of the fed larvae and first stage nymphs 
respectively. 
Reactions to contact with solids. 
At all stages of development, A. ^jei'sicus exhibits a well-marked 
tendency to bring as much of its surface as possible in contact with 
external foreign bodies. This positive thigmotropism is the reason why 
ticks push themselves under any loose solid particles, or into any 
crevices they meet. The most convenient way of demonstrating this 
property is by placing a number of ticks into a large glass vessel 
containing one or two jiieces of filter-paper. If the vessel be left in a 
dark room for a few hours the ticks will all be found congregated under¬ 
neath the pieces of paper. This experiment may be varied by using 
V shaped pieces of paper when the ticks will be found congregated in 
the angles of the Vs, this being the position in which most of their 
surface is in contact with other solids. 
