2 Earlier Views. 



history both of the agamous and of the sexual forms 

 still left to be elucidated. There was no means by 

 which this could be done satisfactorily except by direct 

 experimental breeding. In carrying this out, however, 

 many, practical difficulties occurred, as constantly 

 happens in experiments of this nature, and these served 

 for a long time to delay the solution of the problem ; so 

 for a season at least it was necessary to rest satisfied 

 with a provisional explanation which was in reality 

 little better than a simple hypothesis. 



In the year 1861 an entirely new theory was 

 propounded by Osten-Sacken \ whose investigations 

 into the history of the numerous species of North 

 American oak gall-flies are well known to the scientific 

 world. He believed he had discovered that those 

 species which had hitherto been considered agamous 

 were in reality sexual, but that the males were 

 developed from differently formed galls. If this theory 

 were correct all that remained to be done was to 

 discover which were the associated gall-forms. But 

 further observation did not confirm this view, and 

 Osten-Sacken had to abandon it. 



Some time afterwards, in 1864, Walsh ^, an American 

 entomologist, advanced a totally different opinion. 

 Walsh had obtained out of apparently exactly similar 

 galls, on one occasion individuals of Cynips spongifica 

 of both sexes, and on another occasion females only, but 

 of Cynips aciadata which are quite different in form. 

 Had this observation been correct, and had it been 



^ Stettiner Entomolog. Zeit. 1861, vol. xxii. pp. 405-423. 



^ Proceedings of the Entomological Society, Philadelphia, vol. i. 



