1881.] 



The Prehensores of Male Butterflies. 



23 



net'sing force when that force is about 15 c.g.s. units. It is probable 

 that by increasing the magnetising force sufficiently the signs of the 

 effects would be reversed. 



When torsion is carried beyond the elastic limit the effects become 

 somewhat diminished, and when a permanent twist has been given, 

 and the wire allowed to come back to its new zero of stress, reversals 

 of the magnetising force then give feeble transient currents whose 

 signs are opposite to those of the currents given when the wire is still 

 under torsion. 



In steel the general effect is less than in iron, but steel exhibits 

 hysteresis more strongly. With copper, silver, brass, german-silver, 

 and platinum, no effects whatever could be observed. In all proba- 

 bility the effects are peculiar to the strongly magnetic metals. 



Having described the experimental results, the author proceeds to 

 point out their relation to the discoveries of Thomson, Villari, Wiede- 

 mann, and Hughes, and attempts to explain the production of transient 

 currents by the setting up of a state of circular magnetisation in the 

 wire. Sir W. Thomson's discovery that aelotropic stress developes an 

 aelotropic difference of magnetic susceptibility in iron may be used to 

 account for circular magnetisation by the combined effects of longi- 

 tudinal magnetisation and torsion. In order that the effects should 

 have the signs which they actually had, this explanation would require 

 that the magnetising force must have been, in all cases, below the 

 Villari critical value at which the effects of push and pull on magneti- 

 sation are reversed. It is shown that this may possibly have been the 

 case, and that the same assumption would explain away some of the 

 contradictions between the author's results and the earlier ones of 

 Matteucci. 



The paper concludes with some general considerations regarding 

 the phenomenon to which the name " hysteresis " has been applied. 



VIII. "The Prehensores of Male Butterflies of the Genera 

 Ornithoptera and Papilio" By PHILIP HENRY GOSSE, F.R.S. 

 Received October 12, 1881. 



(Abstract.) 



Anatomists have long ago recognised, in insects, the existence of 

 certain organs, intimately connected with the function of generation, 

 yet perfectly distinct from the organs which perform the proper 

 generative act. They are found only in the male sex ; and are con- 

 sidered to have, as their sole use, the office of seizing and holding the 

 female, during the act of coition. 



In the detailed examination and comparison of these auxiliary 



