198 ANATOMY. 



raised lines run over the whole of this surface from tootli to tooth, 

 and from the elevated ridge to the superior edge, which makes the 

 whole exterior surface even, arid gives it the appearance of a fine file. 

 With this saw-like apparatus the Tenthredo cuts the substance of 

 leaves, letting an egg drop in, which is there developed that it may 

 subsequently feed upon it. The short triangular process forms 

 merely a key-stone to the margins, gaping at the base, and is of no 

 importance to the function of the organ ; but it is necessary to men- 

 tion it, as it is of great consequence in the structure of the sting in the 

 rest of the Hymenoptera. 



If we examine the projecting sting of the Ichneumons, for example, 

 Pimpla (PI. XXIII. f. 12 14.), we first observe the two exterior 

 valves, (f. 14. a, a,) and between them, a fine horny sting which is a 

 little dilated at its extremity (f. 12.). This sting was long considered 

 simple, and even Gravenhorst, in his monograph of the European Ich- 

 neumons, describes it so *. But it also is double ; the upper part 

 (f. 13. a. and 12. .) is channelled beneath, completely smooth, and 

 only at its broader point beset with small teeth ; the lower (the same, 

 ,) much finer portion is a hair-shaped very pointed bristle, which lies 

 within the channel of the superior one; this also is broader in front and 

 lancet-shaped, and fits into a cavity of the upper part of its own shape. 

 There is thus truly a passage in the aculeus, but so narrow an one that 

 no egg can pass down it, and in this cavity how should it move along ? 

 The egg merely slides down the superior channel, and is secured and 

 pushed on by the inferior bristle pressing against the channel from the 

 base towards the apex, pushing the egg above it. But, to refer this 

 structure back to that described in the saw-flies, we must conceive the 

 two internal valves as united in the superior simple half tube, and 

 the bristle as the elongation of the central process at the base of the 

 valves. 



Its structure is still more artificial in Sirex and the Bees. In Sirex 

 (PI. XXIII. fig. 5 11), in which the sting projects, we find likewise 

 the exterior valves (a, fl) and the central aculeus (b). This again 

 consists of the superior channel (c, c,) and the bristle lying within it, 

 which is here double, (d.d.) All three are dilated at their end (f. "]}, the 

 channel is split, and that portion as well as the bristle upon its entire 



" Ichneumonologia Europsea, torn. i. p. 89. " Hsec seta terebra est, et canali ccntndi 

 longitudinal! instructa esse dicitur, per quern ova poueruntur." 



