298 Dr. T. A. Chapman on 



The sheath is easily broken up, but into groups of 

 scales, and separate scales are not easy to demonstrate. 

 It is of elliptic section, its width being rather greater than 

 is its dorso-ventral diameter. 



The butterfly possesses this cylinder on emerging from 

 the pupa, and appears to lose it as soon as pairing is over. 

 One captured in cop. almost always still possesses it, but 

 one taken otherwise very rarely, showing that the females 

 of these butterflies, like those of so many Lepidoptera, 

 remain quiescent and are rarely seen till pairing has taken 

 place. The cylinder is so easily lost that it seems doubtful 

 whether it retains any coherence by the scale attach- 

 ments, and unless one is especially careful, it is more 

 likely than not to be lost in preparing and mounting a 

 specimen that still possesses it. 



I have certainly several times, I fancy frequently, seen 

 specimens in cop. in which the female did not possess the 

 sheath. These may have been second pairings, or the 

 sheath may have been lost before the first pairing. 



The use of this structure probably is to give rigidity 

 and support to the soft structure of the rein in finding 

 its way to the base of the male genital cavity, and to 

 maintain it in position, with some fixity, with the terminal 

 plate in apposition with the aedeagus, so that penetration 

 may take place. How this exact apposition was secured 

 seemed to be rather puzzling, notwithstanding that the 

 rein when full of fluid could be fairly rigid; but this did 

 not explain how the correct position could be secured so 

 rapidly as in fact it is, the actual pairing being apparently 

 a matter of a second or two. The sheath must occupy 

 with great accuracy the male genital cavity, so that the 

 parts properly coincide. 



The special character of the " furca " in the floor of 

 the male genital cavity, appearing to support nothing 

 nor attach any parts together, is probably related to the 

 rein and its sheath. The rein (and sheath) would arrive 

 at once in a position supported on each side by the branches 

 of the fork, and resting in the hollow between them, filling 

 the genital cavity so that the end of the sheath necessarily 

 impinges against the short exposed portion of the aedeagus, 

 and with the knee-like angle between the prop and the 

 rein, at the base of the clasps. Though, no doubt, the 

 difference in details of structure in the different species 

 make this only a general description of the adaptation. 



