DEVELOPMENT 155 



disengaged, and the acid fluid flows from its mouth, wetting the inside of 

 the cocoon. The process of exclusion from the cocoon lasts for as much 

 as half an hour. The insect seems to be instinctively aware [?] that 

 some time is required to dissolve the gum, as it does not make any at- 

 tempt to open the fibres, and seems to wait with patience this event. 

 When the liquid has fully penetrated the cocoon, the pupa contracts its 

 body, and pressing the hinder end, which is furnished with little hooks, 

 against the inside of the cocoon, forcibly extends its body; at the same 

 time the head pushes hard upon the fibres and a little swelling is 

 observed on the outside. These contractions and extensions of the 

 body are repeated many times, and more fluid is added to soften the 

 gum, until under these efforts the cocoon swells, and finally the fibres 

 separate, and out comes the head of the moth. In an instant the legs 

 are thrust out, and then the whole body appears; not a fibre has been 

 broken, they have only been separated. 



"To observe these phenomena, I had cut open with a razor a small 

 portion of a cocoon in which was a living chrysalis nearly ready to trans- 

 form. The opening made was covered with a piece of mica, of the same 

 shape as the aperture, and fixed to the cocoon with mastic so as to make 

 it solid and air-tight; through the transparent mica I could see the move- 

 ments of the chrysalis perfectly well. 



" When the insect is out of the cocoon, it immediately seeks for a 

 suitable place to attach its claws, so that the wings may hang down, and 

 by their own weight aid the action of the fluids in developing and 

 unfolding the very short and small pad-like wings. Every part of the 

 insect on leaving the cocoon, is perfect and with the form and size of 

 maturity, except the pad-like wings and swollen and elongated abdomen, 

 which still gives the insect a worm-like appearance; the abdomen con- 

 tains the fluids which flow to the wings. 



"When the still immature moth has found a suitable place, it re- 

 mains quiet for a few minutes, and then the wings are seen to grow very 

 rapidly by the afflux of the fluid from the abdomen. In about twenty 

 minutes the wings attain their full size, but they are still like a piece of 

 wet cloth, without consistency and firmness, and as yet entirely unfit for 

 flight, but after one or two hours they become sufficiently stiff, assuming 

 the beautiful form characteristic of the species" (Trouvelot). The 

 expansion of the wing is due to blood-pressure brought about chiefly by 

 the abdominal muscles. In the freshly-emerged insect, the two mem- 

 branes of the wing are corrugated, and expansion consists in the flatten- 

 ing out of these folds. The wing is a sac, which would tend to enlarge 



