170 Dr. T. A. Chapman on the 



In some groups success in this matter is easy, why it 

 should be so difficult here is not quite self-evident. It so 

 happens, however, that in several of my preparations I 

 had so nearly succeeded that they practically demonstrate 

 the conditions almost as satisfactorily as had they been 

 quite successful. They demonstrate that the prop and 

 rein are fully extended, that the terminal plate carrying 

 the ostium reaches the extremity of the fixed aedeagus and 

 is penetrated by the eversible membrane therefrom. In 

 examining living specimens, the two insects seem held 

 together by nothing except the pale slender thread of the 

 prop and rein. How this is held firmly to the aedeagus 

 is not very evident, whether it be merely by the eversible 

 membrane that penetrates the ostium, or whether, as the 

 structure of the extremity of the aedeagus seems to suggest, 

 the terminal plate of the rein is held by certain curved and 

 spring-like processes that are very evident in such species 

 as pheretes, semiargus, orbitulus, etc. The clasps do not 

 seem to be used for prehension, at least at the times when 

 my observations were made. Yet their special structure, 

 very nearly identical throughout the tribe, and different 

 from those of any other Lycaenines, show them to have 

 some important function peculiar to this tribe. It seems 

 that this can hardly be other than to take temporary 

 prehension, by grasping the 7th abdominal segment, at 

 the same time causing or assisting the eversion of the 

 prop and rein. 



It may be noted in most of the photographs submitted 

 that these parts are compressed antero-posteriorly and so 

 remain straight, the prop and rein in the same apparent 

 straight line. But in others where they are compressed 

 laterally, of which one of the photographs of hylas (PI. 

 XXXIX) is as good an example as any, there is seen to be 

 a sharp angulation between the prop and rein when they 

 are fully exserted and expanded ; the effect of this would 

 be, that the angle would reach the inferior angle of the 

 male genital cavity at the base of the clasps, whence the 

 rein would be of just the length to reach along the floor 

 of the cavity to the extremity of the aedeagus, which in 

 the Plebeiids is fixed close to the dorsal margin of the 

 floor and close under the dorsal armature. 



When living specimens are examined, all prehension 

 seems in abeyance except by the rein and aedeagus. 

 Whether this is natural, or a result of inhibition by the 



