1878.] 105 



ON THE PUPATION OF THE NYMPSALII)^. 

 BY J. A. OSBORNE, M.D. 



Whilst tliauking Dr. Chaj^mau for bis information on tliis subject 

 in tbe last number of your Magazine, I can by no means accept bis 

 suggestion that tbe membrane described by me " is neither more nor 

 less than the linings of the trachese," because I find it existing along 

 with, and in addition to, these exuviae and those of the alimentary 

 canal, which, moreover, I find not to have any influence in the support 

 of the chrysalis ; also, the attachment of this membrane to the chrysalis 

 is at a point where no spiracle or other opening exists. I send here- 

 with a few specimens, a look at which I think is sufiicient to settle the 

 point. The chrysalis of Vanessa was prepared last year, and is still in 

 good condition ; those of Pieris hrassicce were made a few weeks ago. 

 One of these, in which the larva-skin has been turned inside out, 

 shows the linings of the last tracheal tube on each side, and in the 

 middle the triangular shaped ligament of suspension. Its apex is 

 more pointed than it should be, because its attachment to the chrysalis 

 is at two adjacent points, from one of which it had separated before 

 drying. In removing the specimen, the second point of attachment 

 has now given way also, but the dried skin retains its shape ; and the 

 two whitish points on the chrysalis, to which the membrane was origi- 

 nally attached, may be very easily seen. I do not think this membrane 

 can be made out by simple observation, without a little manipulation. 

 My method was to remove the caterpillar pupating, or about to pupate, 

 from its attachment, lay it on its back, and when exclusion was some- 

 what more than half advanced, whilst making counter extension on 

 the chrysalis, with a pair of pliers to seize the larva-skin on the ventral 

 aspect and gently draw it down over the tail. The caterpillar skin 

 will then turn inside out, like a stocking drawn off the foot, the linings 

 of tbe trachea) may be seen coming out of the spiracles, and that of 

 the intestine from the anus, whilst the tough and persistent " larvo- 

 pupal " membrane will be cleai'ly defined. It is difiicult, however, to 

 preserve it longer than a few minutes, owing to the twistings and 

 writhings of the insect, and its own tendency to rupture after desic- 

 cation, or rather to part smoothly from the chrysalis like the jointed 

 petiole of a leaf ; but when still fresh, considerable force may be used 

 without detaching it, so that the chrysalis will be drawn out threaten- 

 ing to be torn asunder before the ligament will break. At this time 

 of course there is nothing else holding the chrysalis and larva-skin 

 together — no pinching of the folds of the latter between the rings of 

 the former. The membrane is quite sufiicient of itself. 



