214, (August, 



section being nearly semicircular. At the mouth the sides are still more developed, 

 and are even turned in somewhat and approach each other. The ventral plate, as 

 has just been said, is absent, but in its place is a tough, ventricose membrane 

 (sh. m.), which, by bridging over the gap on the under-side of the short, outer 

 portion, completes the periphery of this part of the plate, and gives it all the 

 characters of a sheath ; it is then reflected on to the wall of the abdomen, no trace 

 of it being found covering in the under-side of the long, inner portion. Under these 

 circumstances the outer portion of the plate must be considered in reality as the 

 true sheath, the inner portion being merely a prolongation from it in order to sub- 

 serve the purposes already pointed out. Scattered over the inner half of the 

 membrane are numbers of small chitinous projections — they may almost be called 

 teeth, — which must come in usefully in steadying the parts upon the plant-structure 

 in the process of laying. 



As we saw in Col. ccespititiella that the sheath was not of the same texture 

 throughout, but that some parts were amber-coloured or brown, and others hyaline, 

 these colours representing stronger and weaker structures respectively, so here we 

 find the same saving of material where strength is not needed, and its concentration 

 in the lines of strain and pressure. Except for a narrow faintly coloured portion 

 occupying the whole width at the inner end, the brown part may be said to begin 

 as a pair of narrow bands, one on each side, not much wider than the rods, and con- 

 tinuous with them, leaving a broad hyaline space in the centre of the plate : 

 gradually widening, they nearly meet a little beyond the middle, this spot corres- 

 ponding as near as may be with that part of the ovipositor where the tendency to 

 yield would be greatest. From this point they begin to contract, and, still keeping 

 to the margin, become reduced in the " true " sheath to narrow but, judging by their 

 dark colour, thick belts, and finally dilate again, and meet round the outer end or 

 mouth, having the appearance of being still further strengthened at this point by 

 very fine transverse ribbing. Thus, to meet the longitudinal strain a continuous 

 band in direct communication with the rod travels the whole length of the organ, 

 whilst at points in its course, particularly at the mouth and near the middle, special 

 transverse strength is also given. Running down the centre of the plate is a 

 brown ridge, something like the one in ccBspititiella, which terminates some little 

 distance short of the mouth in a small swelling that gives off a spur or tie-rod on 

 each side, and at the inner end in a singular black arrow-shaped process that projects 

 beyond the plate. From the sides of the " arrow " a part of the massive protrudor 

 muscles of the ovipositor take their rise, the other part coming from the plate itself 

 close to the attachment of the rods. It would doubtless endanger the integrity of a 

 body so long and slender as the plate, were the strain from these great muscles to be 

 concentrated entirely at one end, and the ridge has consequently been devised for 

 carrying some of it away, and distributing it further down the organ. I have already 

 referred to the ribbing round the outer end of the plate, but the structure of the pale 

 central portion in the " true " sheath is even more peculiar, and is at the same time 

 very elegant, for it looks as if it were made up of minute scales, like those of a 



