214 
Sensory Perceptions in Ticks 
The function of Haller’s organ and the means by 
WHICH A TICK FINDS ITS HOST. 
The peculiar sensory structures known as “ Haller’s organs ” were 
first described by Haller in 1881. On account of their superficial 
resemblance to the auditory sacs present on the antennules of various 
Cr\istacea, he sujiposed that they were auditory in function and 
actually described the existence of otoliths in one of the cavities of 
this organ. Lahille, in 1905, was the first to question Haller’s inter¬ 
pretation of their function and as a result of his experiments with the 
female of Boophilus annulatus suggested that they were olfactory 
organs. Previously, however, Batelli (1891) suggested that they 
might serve as a means of perceiving at a distance the hosts on which 
the ticks feed, but this author brings forward no evidence in support of 
his hypothesis. Nuttall, Cooper and Robinson (1908) were the first to 
give an accurate description of the structure of this organ. In Haenia- 
physalis ptunctata it consists of a minute cavity, about 65 jx in diameter, 
containing sensory bairs, and is associated with a specially modified 
region of the hypodermis. It is always situated on the external dorsal 
surface of the tarsus of the first pair of legs. As we have shown, the 
function of this organ is certainly olfactory, but it would be premature 
to state that this is its only function. The presence of Haller’s organ, 
however, is essential to the tick in the discrimination of its hosts 
as may be shown by the interesting results of the following experi¬ 
ments. 
Whilst conducting the experiments on the effects of odorous vapours 
on both normal ticks and those in which the forelegs had been amputated, 
we also tried the effect of placing a vessel of hot water beneath the 
filter paper on which the ticks were walking. In the case of the 
mutilated ticks all showed themselves sensitive to the combination of 
warmth and moisture, and not only this but many of them inserted 
their mouth parts and endeavoured to feed through the filter paper, 
showing that they were unable to discriminate between warm moist 
filter paper and a fowl, their normal host. On the other hand normal 
ticks, although susceptible to the warmth and moisture, never showed 
the least inclination to feed, although they were equally as hungry as 
the others. These results suggested to us a method by means of which 
ticks might be made to feed on any desired liquid, and after various 
