154 The Scottish Naturalist. 



Drvophanta smtellaris with Trigonas}yis megaptera 



„ longiventris „ Spath. Taschenhcrgi 



Aphilothrix radicis „ Andricus nodidi 



Let us see if a consideration of the biology of the species 

 named affords us any reasonable evidence in favour of this 

 rather startling hypothesis. It must be evident for one thing, 

 that if the species are corelated in the way indicated, we ought 

 to find the two forms equally abundant and in close proximity 

 to each other, just as we find the dimorphic forms of Pri7m(la 

 together ; and this must be more especially the case consider- 

 ing the extremely sluggish nature of the Cynipidce. Some of the 

 species no doubt are found in the same vicinity, but with others 

 this certainly does not happen. Trig, megaptera is not uncom- 

 mon in many woods around Glasgow; it is veiy common for 

 instance at Kenmuir Bank, where 'D. scutellaris does not occur 

 at all, nor even within some miles of it ; and it has such 

 a conspicuous gall that it could scarcely be overlooked. 

 Schenck* also states that T. megaptera is very rare, and D. scute- 

 llaris abundant in Nassau, and this I think will be the case 

 generally. S. vesicatrix, again, is a very local species, by no 

 means common, while N. mufiismatis is met with every where. 

 lY. fumipennis is not uncommon, while S. albipes has only been 

 recorded in Britain from the vicinity, of Glasgow. Schenck 

 does not mention j^iw/^(?w«s, while he gives albipes as common. 

 D. lo7igiventris is pretty common, while S. Taschenbergi has not 

 yet been found in this country. A. nodnU and Aph. radicis are 

 undoubtedly found together, yet 1 have no hesitation insayingthat 

 they are by no means related in the way stated by Adler. J^adicis 

 is found developed in the galls from the autumn till early 

 spring, and it then deposits its eggs. This point is clearly shown 

 by our finding the fly about oaks in April ; the galls are found 

 soft, juicy, and white, with a more or less rosy tinge, towards the 

 middle of May, the larvae being found in them till the end of 

 July; all this proving positively that radicis has only one brood 

 in the year. The galls oinoduli, on the other hand, appear in the 

 spring, and the insects quit them in the autumn. In other words, 

 the development of the two species goes on side by side. 

 How then can the one give origin to the other ? But more than 

 that, I have taken a gall oi radicis in the spring and placed it 

 at the root of an oak, where I had satisfied myself the species did 



^ * Beitr. z. Kennt. d. Nassauischcn Cynipiden, 



