POSTSCRIPT. 



However interesting may be the facts of alternation of 

 generations as they occur in the oak gall-flies, I have no 

 desire to ignore those species which live on other plants, or 

 to omit the study of their evolution. 



The rose Cynipidae, of which I have observed three 

 species, Rhodites rosae, eglanteriae, and spinosissimae, are 

 alwa^^s propagated by one annual generation. It is the 

 same with the species of the genus Aidax, A. rhaeadis and 

 A. hieracii; and with those of the genus Diastrophits, D. riihi 

 and D. glechomae. 



On the other hand there is a Cynips on the maple which 

 shows absolutely the same biological cycle as the Cynipidae 

 of the oak. In this species, as in those, one agamous 

 alternates with one sexual generation. 



The following is a description of this insect and the history 

 of its development. 



1. Pediaspis aceris, ¥ovsier= sorb i, Tischbein\ 



Gall. The gall is found on the roots of the sycamore 

 {Acer pseiido-plataniis), but it is also met with on the Norway 

 maple {Acer platanoides). When solitary, the gall is round, 

 like a pea, and about 5 mm. in diameter. When in clusters, 

 these are found embracing rootlets, even those of i cm. in 



^ Dr. Mayr of Vienna, whose works have been of immense ser\-ice 

 to the study of the Cynipidae, had previously suggested that the two 

 species Pediaspis and Bathyaspis aceris were two forms of the same 

 insect. His breeding experiments, like my own, have confirmed this 

 hypothesis. 



