64 SCIENCE PROGRESS. 



rence and are less common than the type forms. Why is 

 this ? 



The case is an interesting one in several ways. Weis- 

 mann has made this species the subject of a good deal of 

 speculation and some experiment. In his earlier paper (6) 

 he regards it as certain that bryonies is an ancient form 

 dating from the glacial period and that napi has been very 

 gradually evolved from it as temperate conditions super- 

 vened. In the later paper (7) from the fact that two male 

 napi and a bryonies female irregularly patched with white 

 emerged from some forced pupae supposed to be all offspring 

 of bryonies, he is apparently disposed to doubt his original 

 view, though, as he points out, the napi may have been merely 

 introduced larvae and the blotched specimen may have been 

 gynandromorphous. The possibility that there may be dis- 

 continuity is not considered. Moreover, the matter is 

 greatly complicated by the fact that bryonies is not, as Weis- 

 mann states, exclusively one brooded, for I have reared sum- 

 mer broods, emerging in August, both from bryonies females 

 caught at Fobello (3000 feet) and above the Tosa Falls 

 (5500 feet). The former were flying with napi, and for 

 anything I know these summer emergences may have had 

 a napi father. 



Those from Tosa may also have been cross - breds, 

 though this is less likelv. All the second brood from Fo- 

 bello were intermediate and some of those from Tosa are so 

 also, though the rest of the latter are bryonies. It appears 

 therefore to be possible that the intermediates found wild 

 may be a second brood from bryonies. In order to deter- 

 mine this it would be necessary at least to have statistics 

 from one locality extending over the whole period during 

 which the species fly. 



The view that napi has been very slowly evolved from 

 bryonies or bryonies from napi is not easy to reconcile with 

 the facts of the present occurrence of the forms. Bryonies is 

 met with in the far North and again in the high Alps. If 

 napi has been continuously evolved from it, passing through 

 a long series of intermediates as normals, we should expect 

 that those places in Europe which have a climate inter- 



