METAMORPHOSIS IN LEPIDOPTERA. 23 



hitched into a fold of the larval skin, and must thereby give increased 

 security to the suspension of the pupa. In Dr. Osborne's specimens a 

 triangular ligament is shown by the reflection of the skin backwards, 

 the triangle having its apex at these tubercles, and consisting of the 

 double fold of the skin, the anterior portion being thrown back over 

 the truly suspensory portion." Edwards confirms (Canadian Knto- 

 moloyist, vol. ix., pp. 224 et seq.) the presence of the " Osborne 

 membrane " in Polyyonia {Grapta) interroyationis and Anoxia archip- 

 jms, describing it, in the former, as " a narrow, white membrane or 

 ligament, about one-tenth of an inch long, one end of which is pointed 

 and fastened to the inner side of the larval skin near the extremity 

 thereof, and the other forked and fastened to the ends of two curved, 

 slightly raised, longitudinal ridges, which are to be found on the ventral 

 side of the last segment. These ends are at the anterior edge of the 

 segment." He adds that "in A. archippus the ligament is much 

 larger and stronger than in Polyyonia, and is broad, black, and deeply- 

 forked Avhere it is attached to the segment. In this species, instead of 

 low ridges, there are two rows of shiny black processes, three in each 

 row, and the outer pair are knobbed and a little pointed anteriorly. On 

 these outer knobs the ligament is fastened." Edwards further notes 

 that he does " not believe that the chrysalis of Polyyonia ever seizes 

 the loosened skin for a support" the support that such a hold could 

 furnish not being essential, for "the skin can be raised with forceps 

 entirely from the abdominal segments on the ventral side, so as to 

 discover the distended membrane," or the skin "may be cut off just 

 below the membrane at the instant the effort for freeing the tail 

 begins." In these last cases "the chrysalides are seen to be con- 

 nected with the skin by the membrane only, and the membrane is the 

 only lever by which the chrysalis climbs to the skin. There cannot 

 possibly be any other support." This brief summary Edwards follows 

 up by an excellent detailed description of the mode of pupation in 

 Polyyonia interroyationis and Anosia archippus, much too long, how- 

 ever, even to summarise here. One point, however, raised by Edwards, 

 should be noticed. He says : " The last act of pupation is beyond my 

 comprehension, viz., the rising of the chrysalis with no external aid, 

 save that which comes from the ligament." This is probably effected 

 in two ways, viz., by the flexibility of the terminal segment, and by 

 the growth of the cremaster which occurs at this period. 



Later observations on pupating Aylais urticae are detailed (Ent. 

 Mo. May., xvi., pp. 55-5b) by Osborne. He notes the " Osborne 

 ligament" as being formed by the coalescing of the two folds of the 

 transparent inner coat of the larval skin. He says that " this inner coat 

 is elastic, very distensible, and of a semiplastic consistence, and readily 

 runs into the ligamentary form under the influence of tension alone. 

 In A. urticae the two crescentic whitish ridges embracing the anal area 

 terminate anteriorly in horns, which project over the segments imme- 

 diately in front. These horns have, on the inner side, a black knob, 

 terminating a black line which runs along the under inner side of 

 each ridge, and separated from the rest of the horn (the outer whitish 

 knob) by what seems a small groove. It is to these black knobs alone 

 that the ligament is finally attached, and when the tension is great and 

 prolonged the corners of the ligament are pouched out by them into 

 hooks or shallow pockets. But the adhesion of the pupa to the liga- 



