336 Comparative Classification of Cynipidae. 



tion. Therefore by attending only to outward differences, 

 we may seek out the subtlest distinctions, and yet 

 obtain no certain basis for a true classification. 

 Hitherto, for example, the sexual generations belonging 

 to Neuroterus and Dryophanta have been united in 

 the genus Spathegasier ; but one could no more unite 

 two agamous genera, Neuroterus and Dryophanta, into 

 one genus, than they could the two forms of Spathe- 

 gaster. It certainly cannot be denied that the two 

 Spathegasier forms are alike in outward appearance, 

 but the two ovipositors show an important difference : 

 and it is on this character that their separation must 

 be based. It may be objected that a distinction based 

 on the form and structure of the ovipositor is too 

 subtle, but there is no other constant distinguishing 

 mark. The genus Biorhiza also contains heterogeneous 

 species. Biorhiza aptera and Biorhiza renum resemble 

 each other only in outward appearance ; their ovi- 

 positors are very unlike : and the two sexual genera- 

 tions belonging to them are so different that they 

 could not possibly be united in one genus. 



Besides the assistance in differentiation which the 

 ovipositor affords, the manner of gall formation offers 

 an excellent criterion for determining associated species ; 

 and with a proper regard to these two features, the 

 classification of the Cynipidae may be successfully 

 accomplished. It must be hailed as a step in advance 

 that analytical tables have been constructed on this 

 basis ; Schlechtendal \ for example, has sketched out 

 a key to the Cynipidae based on their galls. 



^ R. V. Schlechtendal und O. Wiinsche, Die Insekten, 1879. 



