THE AMERICAN ENTOMOLOGIST. 



f6s 



limb. They vary much in form, and may 

 be more or less obsolete. 



Fourthly. Between them is what may be 

 called the rectal piece {r p\ consisting of a 

 piece more or less well marked and ele- 

 vated, especially around the closed rectum. 



It is principally by the leverage obtained 

 by the hooking of the sustainers in the re- 

 taining membrane, which acts as a swing- 

 ing fulcrum, that the chrysalis is prevented 

 from falling, after the cremaster is with- 

 drawn from the larval skin. It is also 

 principally by this same means that it is 

 enabled to reach the silk with the cremas- 

 tral hook-pad. Yet the rectal ligament 



(Fig. 67.) 



Ideal representation of the anal subjoint of the larva of 

 Vianessa antiopa, from behind, with the spines removed and 

 all the parts forced apart by pressure so as to show the homol- 

 ogies of the parts in the chrysalis which are concerned in pu- 

 pation ; the homologies indicated by corresponding letters in 

 Fig. 68, except that r (the rectum) corresponds with / r in 

 Fig. 68 (after Riley). 



plays a most important part, and in some 

 species a more important part even, in my 

 estimation, than the membrane itself. The 

 tracheal ligaments, which, from a study of 

 specimens plunged in alcohol when the 

 larval skin was about half shed, I was at 

 first inclined to believe important auxili- 

 aries, are, I am now satisfied, of very little 

 or no service in most cases. The rectal 

 ligament is a constant physiological factor, 

 and its importance cannot be ascertained 

 by attempts to sever the membrane at the 

 critical moment, because in such attempts 

 the ligament is more or less drawn out be- 

 yond the power of the sphincter muscles in 

 the chrysalis to control it. 



Dissected immediately after suspension, 

 and the subjoint of the larva will be found 

 to be bathed, especially between the legs 

 and around the rectum, in an abundance 

 of translucent, membranous material. An 

 hour or more after suspension the end of 

 the forming chrysalis begins to separate 

 from the larval skin, except at the tip of 

 the cremaster (see Fig. 70, b). Gradually 

 the skin of the legs and of the whole sub- 

 joint stretches, and with the stretching, the 

 cremaster elongates, the rectal piece re- 

 cedes more and more from the larval rec- 

 tum, and the sustentor ridges diverge more 

 and more from the cremaster, carrying 

 with them, on the sustainers, a part of the 

 soft membrane. If a larva be carefully 



(Fig. 68.) 



Anal parts of chrysalis of Vanessa antiopa^ just prior to 

 final extraction from larva skin : c, cremaster ; chp, cremas- 

 tral hook-pad ; h, one of the hooks more enlarged ; vir^ ven- 

 tral cremastral ridge ; dcr^ dorsal cremastral ridge ; /r, larval 

 rectum ; /r, pupal rectum ; r/, rectal plate ; sr^ sustentor 

 ridges ; .r, sustentores • 7«r, membrana retinens r/, rectal 

 ligament ; ^/, tracheal ligament ; the nth or last spiracle-bear- 

 ing joint and the 12th joint being numbered (after Riley). 



dissected at this stage, the forming mem- 

 brane may be raised with the point of a 

 needle and stretched so as to show its con- 

 nection with the rectal ligament (Fig. 70, d')\ 

 or it may be lifted entirely from the retain- 

 ers, when, by its elasticity, it contracts 

 and becomes more or less fully absorbed 

 in the rectal ligament (Fig. 70, e). It is at 

 this stage that the strength of the latter 

 may l)e fully tested, and if, after the larval 

 skin and retaining membrane are carefully 

 removed without loosening the rectal liga- 

 ment, the chrysalis be grasped in the neigh- 

 borhood of the rectum so as to supply the 

 natural holding power of the sphincter mus- 

 cles, the ligament will sustain, as I have 



