22 BRITISH LEPtDOPTERA. 



<fcc, and had also demonstrated the existence of this spiracle in the 

 imagines." 



The action of the suspensory processes (in suspended pupae) at the 

 time of moulting was demonstrated (Nature, vol. xvi., pp. 502-503) by 

 Osborne, who also discovered that the final connection between the old 

 larval skin and the pupa of Ai/lais urticae, at the critical moment that 

 the latter has to insert the cremastral hooks into the pad of silk already 

 prepared for it, was "a membrane extending from the lining of the 

 old larval skin to the anterior horns of the two lateral ridges bounding 

 the anal area of the chrysalis." He found this in Pterin brassicae and 

 Euchlo'e cardamines, as well as in Ar/lais urticae, and by cutting the girt 

 or loop by which pupating larvae of the two first-named are supported 

 during this period, he changed many pupating larvae from Succincti 

 into Suspend, and found that a third or fourth of the Pieris were able 

 to attach themselves by the cremastral hooks to the silk in the manner 

 of true Susjiensi. He observed that the method by which this was done, 

 in the thus artificially- suspended Pierids, is essentially the same as in 

 Aglais urticae " except that the rapid and assured precision with which 

 the Vanessid chrysalis thrusts up its cremaster and lays hold upon the 

 silk, is replaced, in the Pierids, by long and laborious efforts as if the 

 tail were just a little too short to reach the silk." He further noticed 

 that, in the Anthocarid, not one individual, of which the girt had been 

 previously cut, fell whilst pupating, but that, in all (seven), the pupal 

 cremaster was retained in the pocket of the old larval skin, so that 

 suspension was directly from the latter. Six other larvae, that had not 

 been interfered with, became Suspend of themselves, attaching them- 

 selves exactly as those in which the girt had been cut, viz., by the 

 cremaster being still retained within the exuviae of the old skin. 



Osborne considered that the suspension of Euchlo'e was due to the 

 membrane (described above as being present in A. urticae) persisting 

 unbroken, and states that he has " tested its strength to sustain the 

 weight of the chrysalis." He adds that " the final writhings of the insect 

 are not to get rid of the old larval skin, but to rupture this membrane 

 after the chrysalis has made good its tail attachment to the silk." We 

 have observed pupae of Pieris rapae, Aporia crataeiji and Gonepteryx 

 rhamni suspended in a similar manner. Further details as to this 

 membrane and its action are given (Ent. Mo. 2la<j., xv., pp. 105-106) 

 by Osborne, and he suggests that the membrane is a persistent and 

 specialised portion of the general subcutaneous connective tissue, 

 persistent, in part, for want of a point cVappui from which to act upon 

 it before the tail of the chrysalis is fixed, &c. He further notes that, 

 in another experiment on pupating larvae of Pieris brassicae, no less 

 than 200 pupae succeeded in fixing themselves by the cremaster as 

 Suspensi, whilst 150 fell down, having failed to reach the silk with 

 their books. This, he considers, was probably due to some difference 

 in the relative length of the cremaster and membrane. Chapman, 

 commenting on this " Osborne membrane," says (loc. cit., p. 136) that 

 "the last abdominal segment consists of two portions (strictly two 

 segments), the segment proper and the anal tubercle, the latter forming 

 the hook-covered tubercle by which suspension takes place, and the 

 segment proper being reduced on its ventral aspect, in the pupa, to a 

 narrow line presenting two distinct, small, rounded tubercles. In the 

 specimens prepared by Dr. Osborne, these tubercles are distinctly 



