G. H. F. Nuttall, W. F. Cooper and L. E. Robinson 239 
(1907), and Hooker (1908)). Regarding the structure of the organ, 
Lewis (1892) in a few cursory remarks on the subject, adds nothing to 
the information to be obtained from Haller’s account. Martin (1895, 
p. 273, see Plate XIV, fig. 8) observed three vesicles on leg 1, in 
Amblyomma qvantini: the median vesicle was described as spherical 
in shape and contained a small compact mass—apparently an otolith ; 
the other two vesicles contained hairs only. Donitz (1907) summarises, 
in three paragraphs, our knowledge of the structure and function of 
Haller’s organ, up to that time. 
In the course of our work on the Ixodoidea, we have investigated 
the anatomical structure of the organ in every genus, and we have 
come to the conclusion that Haller’s description is erroneous in many 
respects, hence the present communication. 
Throughout the entire super-family, the principal features of the 
structure of Haller’s organ are sufficiently constant, that, for present 
purposes, a description of the organ as exhibited in Haemaphysalis 
punctata, after making due allowance for generic and specific differences 
in details, will suffice as a guide to all. 
Haller’s organ is a minute cavity or vesicle (diameter about (15 p) 
containing sensory hairs and associated with specially modified hypo- 
dermal tissues which lie immediately beneath it. It is borne on the 
dorsal surface of the terminal article (tarsus) of the first pair of legs; 
Haller’s statement that it is borne “auf der Bauchflache der Extremitat’’ 
is incorrect. It bulges down into the interior of the leg, its surface being 
Hush with the surrounding parts, and is formed entirely of chitin which 
is continuous with the chitinous cuticle of the leg. The superficial part 
or roof of the vesicle is formed of thin transparent chitin, through which 
a minute slit-like pore opens (Fig. 1, p. 240), establishing communica¬ 
tion between the interior of the vesicle and the external air 1 . In lateral 
view (Plate XVIII), as usually seen in mounted specimens of the tarsus, 
1 Knowing well the difficulty of correctly interpreting the real nature of minute 
structures formed of highly refractive chitin, especially in the case of a minute and thin- 
lipped pore, we have succeeded in demonstrating the patency of this opening in a fairly 
convincing manner. A leg of the first pair was snipped off a living tick, with scissors, and 
immersed in a syrupy solution of Canada balsam on a cover-glass : this was inverted over 
a small glass chamber mounted on a glass slip, in the manner of a hanging-drop preparation. 
A small lateral tube opening into the chamber made it possible to connect the apparatus 
with an air-pump, the excess of balsam on the cover-glass forming an efficient luting to 
form an air-tight fitting. The apparatus was placed on the stage of the microscope, and 
after sharply focussing the pore of Haller’s organ, the air was slowly exhausted. In 
every case, immediately exhaustion commenced, a bubble of air was seen to exude from the 
pore. 
