DEVELOPMENT 143 



T. polyphemus is "provided with two glands opening into the mouth, 

 which secrete during the last few days of the pupa state, a fluid which is 

 a dissolvent for the gum so firmly uniting the fibres of the cocoon. This 

 liquid is composed in great part of bombycic acid. When the insect has 

 accomplished the work of transformation which is going on under the 

 pupa skin, it manifests a great activity, and soon the chrysalis covering 

 bursts open longitudinally upon the thorax ; the head and legs are soon 

 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 re- 

 peated 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 un- 

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

 sect on leaving the cocoon, is perfect and with the form and size of ma- 

 turity, 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 



