Aphilotrix-Andricus Croup. 133 



which is covered by this papilla, and between the two 

 papillae of the posterior plates, we find the aperture of 

 the anus. The shorter the ovipositor,, the nearer to the 

 end of the plate is the papilla ; the longer the ovipositor, 

 the further up »is the papilla situated ; we should 

 accordingly expect to find in Andricus noditlt 3. relatively 

 long ovipositor. We also know that Andricus noduli 

 must bore through the bark, in order to reach the 

 cambium-ring, therefore the ovipositor must be long 

 enough to penetrate a depth of 2 mm. It measures 

 about 2-5 mm., and is thus longer than the whole fly. 



In other species of Andricus^ a relatively short 

 ovipositor is found, and consequently the papilla is 

 placed nearer the end. This can be recognized in 

 the ovipositor oi Andricus cirratiis (Fig. i). It enables 

 the fly to bore into the winter buds while small and 

 scarcely developed ; and in these it is only necessary 

 to penetrate at the furthest 0-5 mm. in order to place 

 the ^%% in the centre of the bud-axis. 



The longer the ovipositor the greater, relatively, will 

 be its spiral curvature ; but in order that the passage 

 of the rectum may suffer no infraction, it must always 

 occupy the same position; therefore its aperture is 

 sometimes nearer, and sometimes farther from the ends 

 of the plates of the ovipositor. An examination of the 

 figures in Plate III shows that the length of the plates 

 and of the ovipositors are always the same, because the 

 small processes of the posterior plates form the sheath 

 of the ovipositor, and enclose it when at rest. 



However similar in some cases the ovipositors of 

 the two generations may appear, there is a constant 



