240 
“ Haller's Organ ” in Ticks 
the cavity of the vesicle is seen to be divided by folds or thickenings of 
its chitinous lining, into two chambers—a smaller superficial chamber 
from which the above-mentioned pore opens to the exterior, and a larger 
chamber, the floor of which, on the side towards the proximal end of the 
tarsus, is raised into a number of shallow conical papillae (Plate XVIII, 
Fig. 1), each of which bears a sensory hair. The sensory hairs are 
straight and stiff and protrade across the cavity of the larger chamber, 
their points being directed towards the irregular and indefinite opening 
between the two chambers. The sensory hairs are 20—25yu, in length 
ACCESSORY PIT—4~h—. 
ROOF OF VESICLE OF 
HALLER’S ORGAN.— - 
WALL OF VESICLE.-! 
SENSORY HAIRS 
PAPILLAE 
\ -PROTECTING HAIRS. 
Vf 
PSEUDO-ARTICULATION 
UA--SLIT-LIKE PORE. 
^PROTECTING HAIRS. 
Fig. 1. Haller’s organ as seen from the dorsal aspect. x330. (L. E.E.) 
and differ in their appearance from the other hairs on the body 
and appendages of the tick: the internal cavity of each is compara¬ 
tively large, the bounding walls are unusually thin, and there is no 
constriction at the base, the contour of the shaft of the hair merging 
into that of the basal papilla without any perceptible line of demarca¬ 
tion. 
With regard to the structure of the hypodermis underlying Haller’s 
organ, we have been limited to a study of sections, the material for which 
was preserved by methods unsuitable for the determination of the 
structure of delicate cellular elements, and until new supplies of living 
