130 Comparative Classification of Cynipidae. 



each other, they could never be mistaken in spite of 

 considerable similarity of colouring. The size may be 

 nearly the same, but the form of the thorax, the cut of 

 the wings, and the configuration of the abdomen are 

 so different, that it would be impossible to confound the 

 two insects. These outward differences are still further 

 confirmed by the form and structure of the ovipositor. 

 The delicate little ovipositor of Spaihegaster takes up 

 very small space, while the long spirally-coiled ovi- 

 positor of Neuroteriis requires the whole abdominal 

 cavity to contain it, and hence the difference in the 

 contour of the abdomen. Again, the manner in which 

 Spaihegaster bores into the leaves requires a greater 

 mobility of the abdomen, and so we find it is distinctly 

 pedunculated ; Neuroterus on the contrary is almost 

 sessile. Lastly, Spaihegaster selects only leaves of very 

 tender consistence in which to lay its eggs, and must 

 consequently be able to fly easily; we find Spaihe- 

 gaster therefore provided with longer and broader 

 wings than Neuroterus, which can ever}^where find buds 

 in which to lay its eggs, and needs no particular power 

 of flight. While in a manner we can thus construct 

 the whole insect from the ovipositor, it is also possible 

 to distinguish with certainty the various genera by its 

 different methods of action. If two alternating genera- 

 tions live in perfectly distinct outward conditions, it 

 is absolutely essential that the ovipositor should 

 accommodate itself to them, and take that form which 

 is most suitable for the proper insertion of the eggs. 

 If one generation appears at a season when there are 

 only buds to be found, it must be provided with an 



