THE ACT OF PUPATION. 1693 



EXCURSUS LXXL—TUE ACT OF PUPATION. 



The Imtterllv has liiiii.; a\v;iv 

 The shell thtit hound it fa'st, 



And sereeiied it from the ehilling hrecze, 

 The winter's hitter hlast. 



('UA\vi-i;iu>. — '/'//<' Sunn;/ S'Hminer Months. 



Tin: elumges umlorgoiie by a biittcrHy in passing from the caterpillar to 

 the chrysalis state have always excited great interest ; yet, notwithstanding 

 all that has been written on the subject, mostly modelled upon the detailed 

 but not wholly accurate account given more than a century ago by Keau- 

 miu-, the method by which the chrysalis inclosed within the larval skin 

 becomes attached to the silken pad into which tiie hindmost feet of the 

 caterpillar had previously been [)huiged, has never been rightly explained 

 until within a dozen years, when the observations of Osborne in England, 

 and of Edwards, and especially of Riley,* in our owncoimtry, have solved 

 the problem. The process is the most extraordinary in the higher butter- 

 flies, which suspend themselves in pupation by the hinder end only, without 

 first spinning a loop, like other butterfly larvae, for the support of the an- 

 terior, heavier part of the body. 



A cater[)illar of this kind preparing for pupation spins a loose mass of 

 silk in some suitable place, and, firmly attaching itself to It by the hooks 

 of the anal prolegs and the spines at the edge of the last abdominal seg- 

 ment, casts itself loose from all other su[)p(>rt, and Iiangs by the tail. It 

 next curves the front part of its body tipward on the ventral side, and by 

 and by, when the front part of the body has become greatly swollen by the 

 descent of the Ijody tluiils, and after mmy writhings and contortions, a rent 

 is produced in the back of the caterpillar, and the chrysalis gradually pro- 

 trudes ; not as it will afterward appear, but a limp, soft, and rather shape- 

 less mass. It now hangs at full length, and the thin integument of the 

 caterpillar, by the shrinkage which necessarily follows its drying, aided 

 more or less by the alternate contraction and extension of the chrysalis, 

 creeps back toward the button of silk to which it is attached ; but its ter- 

 minal portion with the cremaster and the cremastral hooks, destined to be 

 plunged in the pad of silk from which it has been suspended, still lie within 

 the cup-shaped, crumpled pellicle ; the miracle is, how it is to get outside 

 of it and not drop to the ground ; the wonder, why, when the skin has left 

 half the chrysalis exposed, and that the stoutest and heaviest half, it does 

 not drop out forthwith. 



Reaumur gave a very circumstantial account of the changes in one of 

 the European Xymphalidae, and his statement has l)een copied by many 

 and repeated by others who have witnessed the process for themselves, but 

 with his eyes ; he asserted that the retreating larval skin was gripped be- 



*I owe to Mr. Rilev's kindness the cuts introduced here. 



