238 
ON THE STRUCTURE OF “HALLER’S ORGAN” IN 
THE 1XODOIDEA. 
By Prof. G. H. F. NUTTALL, F.R.S., W. F. COOPER, B.A. 
and L. E. ROBINSON, A.R.C.Sc. 
(Plate XVIII and one Text Figure.) 
In the year 1881, G. Haller published a description of the sensory 
organ of ticks which has since borne his name; he was apparently so 
much impressed by its remarkable similarity in structure to the auditory 
organs of many Crustacea, that he assumed it to be an organ of hearing, 
and even went so far as to describe the presence of otoliths within one 
of the cavities of the organ. Since that time, other zoologists appear to 
have given little attention to this structure, the majority of those who 
have had occasion to mention it, contenting themselves with a brief 
resume of Haller’s observations and a reference to his paper. 
The first to question the accuracy of Haller’s interpretation of the 
function of the organ, was Lahille (1905), who published the results of 
numerous experiments made on living specimens of the South American 
Cattle-tick, Boophilus annulatus var. microplus. The conclusion which 
he drew from his observations was, that the function of Haller’s organ 
is olfactory and not auditory. Lahille’s observations concern only the 
function of the organ ; he gives no anatomical description. Batelli (1891) 
calls attention to the fact that ticks frequently move their first pair of 
legs (bearing Haller’s organ) in the manner of the antennae of insects, 
and suggests that the organs serve as a means of perceiving, at a distance, 
the presence of the host-animals which are so indispensable to their 
existence. He also points out the remarkable resemblance of Haller’s 
organ to the sensory organs described by F. Dahl (1885), occurring in 
Pachygnatha listeri, but, after an examination of Dahl’s description and 
figures, we think that the points of resemblance are somewhat remote. 
Other observers have alluded to the antenna-like movements of the 
first pair of legs in ticks (vide Wheler (1899, 1900), Hunter and Hooker 
