26 Observations on Cynipidae. 



If we compare the flies of the two generations 

 belonging to any of the species above described, we 

 shall find the differences at first sight very slight. The 

 difference of colouring is unimportant, and is chiefly 

 observable in a slight variation in the colour of the legs ; 

 nor is the size of the body very different, while the 

 form and surface markings agree in many points. At 

 the same time it is not difficult to distinguish the one 

 generation from the other, indeed if the two were placed 

 side by side it would be difficult to mistake them, 

 iheir bodily conformation being totally different. The 

 Neuroterus is more compressed, the abdomen much 

 more developed, the wings shorter than the length of 

 the body, the antennae about two-thirds of the latter. 

 The Spathegaster, on the contrary, is more slender, 

 has longer and narrower wings, which always exceed 

 the length of the body; the antennae are somewhat 

 less than two-thirds of the length of the body; and 

 lastly the abdomen is not so strongly developed. 

 The configuration and size of the abdomen depend 

 entirely on the size and form of the ovipositor. 

 When the ovipositor is of great length, as in Neuro- 

 terus laeviusculus, it lies in repose spirally coiled in 

 the abdominal cavity; and from the greater space 

 which such an ovipositor requires, a larger abdomen 

 becomes necessary. In Spathegaster, the alternate 

 generation, the ovipositor is totally different, being small 

 and slender; and since it occupies little room within 

 the body we naturally find the abdomen altered in form. 

 This dift'erence in the form of the ovipositor is a constant 

 one, even when the two generations are otherwise much 



