61 



JSToTE ox A Remarkable Stigmatic Organ in the Nymph of 



Ornithodoros megnini (Duges). 



By E. G. Wheler. 

 {Read Octoher IdtJi, 1900.) 



On August 27tli last, Mr. A. E. Shipley, University Lecturer 

 at Cambridge, sent me two specimens of the above species of Tick, 

 one of which was slightly, and the other more fully distended. 

 The latter was alive. 



The letter which accompanied them stated that they had 

 been taken by Dr. J. Christian Simpson out of the ear of an 

 American visitor to Cambridge, who had spent some time camping 

 out in Arizona during the early summer of this year. If, as the 

 American thought, the ticks were acquired whilst on this expe- 

 dition, they must have been in the external auditory meatus for 

 many weeks. They gave rise to little or no inconvenience. 



On my referring to Professor Neumann, of Toulouse, he at 

 once identified them as Ornithodoros (or Argas) megnini. This 

 form belongs to the Argasinae, but a careful examination showed 

 a very remarkable diflference from other members of that sub- 

 family of the Ixodidae, and such as appears to be another instance 

 of those extraordinary variations of type that have already made 

 the study of these parasites unusually interesting. 



The feature referred to consists of two protuberances placed in 

 the position of stigmata, one on each side of the body. They are 

 situated above, instead of behind the fourth pair of legs, and 

 are therefore visible from the dorsal side of the tick. They are 

 entirely different from the stigmal plates and peritremes usually 

 present. The top is truncate and perforated with a large hole, 

 through which, in the living specimen, was to be seen a pointed 

 organ, projected and withdrawn at will with considerable 

 rapidity (Figs. 1 and 2). This organ only partially filled up the 

 orifice; it was furnished with three hairs at the end (Fig. 1), 

 and in appearance was somewhat similar to the terminal joints 

 of the palpi. 



