CURRENT NOTES. 107 



reflection on Herr Heyne, who would no doubt have recognised what 

 they were, had he really examined them, but as showing what a close 

 resemblance there is between the two pupa-cases ; I have placed with 

 them some genuine Cochlidid cases, with their cocoons, to illustrate this. 

 The resemblance is, however, not merely of appearance, but functional 

 also. The moth-pupa, i.e., the moth itself inside the pupa-case, 

 almost certainly by inflating itself with air, to secure greater 

 size and a stifitened epiderm as a basis of muscular action, exerts an 

 end-to-end pressure within the cocoon, and so forces off a lid. This lid 

 is not prepared by the larva, in any special sense ; the cocoon is brittle, 

 and the form of the cocoon makes this lid the easiest line of fracture 

 under the forces exerted. This is seen to be the case by the fracture 

 being somewhat irregular and different in each cocoon, and may be 

 proved experimentally, as I will immediately mention. The fracture 

 is also determined at the precise line in which it occurs, and the forces 

 acting upon the cocoon are intensified at one point, so as more easily 

 to start the fracture, by the sharp beak (or ' cocoon-opener ') with 

 which the pupa is armed. This beak acts, not by cutting, but by 

 bringing the strain on the cocoon to a more definite focus at one point. 

 The experiments I refer to are simply this : if a sound cocoon be taken, 

 and with say the point of a penknife, an attempt be made to remove 

 such a lid, a fracture starts at the spot where the penknife is applied, 

 and a lid at once breaks off. This lid is very similar to the one the 

 moth makes, but is less symmetrical, and may be considerably larger 

 or smaller than it is, and always starts at the point whei'e a pressure 

 is applied by the sharp implement. It is, therefore, similar to the lid 

 the moth makes, but not the same lid, and shows that such a lid occurs 

 wherever the forces applied determine, and not along a specially- 

 prepared line. The experiment is, indeed, even more conclusive than 

 this. It is not always easy to say of a sound cocoon, which end is 

 which, and if the wrong end be attacked, a lid is removed just as 

 correctly as at the right one. It is here that the beak or ' cocoon-opener ' 

 is useful as determining that the fracture shall be at the right end, 

 making the lid split oft' here, under much less pressure than would be 

 efficient without it, and leavins: no chance for fracture to occur at the 

 wrong end where pressure is equally distributed. The Sy.ttroptis breaks 

 off a similar lid, no doubt by similar end-to-end pressure to that 

 exerted by the moth, Diptera having the habit of inflating themselves 

 with air, at emergence from the pupa, highly developed. This pupa 

 also has a beak very like that of the Cochlidid, but even stronger and 

 sharper. I have put in the box a Bombyliid pupa-case from West 

 Africa which is very like some British forms. The head armature is 

 not a ' cocoon-opener ' but an excavating or navvying machine, for use 

 in burrowing a way out of loose soil, such as solitary bees' nests are 

 found in. Prof. Westwood gave a monograph of the genus Si/stropus 

 in our Transarticms for 1876, and described and figured the pupa of an 

 African species of practically the same habits as this South American 

 one. Mr. J. E. Collin, m further illustration of Dr. Chapman's 

 remarks, exhibited specimens of : (a) Systrapus, sp. ? from Buenos 

 Ayres, parasitic on a Bombycid Lepidopteron (Cochlidid?). This he 

 said was possibly the same as Dr. Chapman would have reared from 

 his cocoons. The species was apparently undescribed, but most allied 

 to 5. brasilienm, Meg. As Prof. Westwood noticed in 1876, the 



