254 



[Seiitcinber, 



has little scales of this material disposed in lines, which radiate from 

 the middle line of the dorsum and pass diagonally downwards. Four 

 or five of these lines, where they meet over the back of the structure 

 at its inner end, are converted into rows of tiny teeth, pointing back 

 towards the abdomen. I imagine that their use is to catch hold of 

 the wall of the pocket, and prevent the root of the sheath from 

 slipping out, when the rest of the apparatus is withdrawn, which, as 

 we shall see presently, happens several times during the operation of 

 cutting the pocket. In consequence of the flexibility of the sheath, 

 the protrudor muscles of the ovipositor, which we have so far always 

 found to spring from the segment immediately above, namely, the 8th 

 or its equivalent the sheath, have here to be moved up to the 7th 

 segment, from the dorsal plate of which at its outer end they take 

 their rise. But a still more remarkable result is the dislocation of 

 the outer rods (Fig. 12) and their transference to the ventral plate of 

 the 7th segment. They could exercise little or no control over so yield- 

 ing a body as the sheath, whereas, by their insertion into the ventral 

 plate of the 7th segment, they are able, as has already been shown 

 (ante, vol. i, p. 150), in the first place to open the outlet, and next to 

 advance the point of the plate into the mouth of the leaf-pocket, and 

 keep it on the stretch, so as to prevent the nipping of the sheath, and 

 of the tender under-parts of the ovipositor, which would else occur. 



The anomalies of the ovipositor are almost as remarkable, and certainly more 

 difBcult to understand. The skeletal portion consists mainly of a very strong hori- 

 zontal plate, flat, except for a rather sharp upward curve at the extremity, and 

 armed with saw-like teeth round its lancet-shaped end (Fig. 10) ; its length, as com- 

 pared with that of its rods being as nearly as possible 1 to 3. (As the details are 

 not quite alike in all the species, I ought to say that the particular one here de- 

 scribed is semipttrpurella.) I originally called this plate the knife-blade, but it 

 would be more correct to liken it to a pair of knives (sub-plates), lying back to 

 back, and united to each other near the points. The backs of the knives are directly 

 n _ continuous with the rods, and are of 



some considerable thickness up to 

 some little distance from the ex- 

 tremity, when they get spread out 

 and united with each other, leaving 

 only a thread or two of thicker 

 Si'sW material to run on into the tip. 

 The blades, which commence ab- 

 ruptly, are narrow plates of a 

 peculiar fibrous structure, looking 



Fig. 9. 



Fig. 9. — 1, The two halves of ventral plate of ovipositor, with the connecting membrane studded 

 with teeth. 2, dorsal view of the end segments, showing the shape of knife-plate at 

 work. ;i, Inner end of sheath with rows of teeth, and the bifid tip of 7th dorsal plate. 



