1914] Weiss—Thermal Conductivity of Cocoons 49 
a ] 
submerged in water for seven hours, showed interiors perfectly 
dry, the water having penetrated only the outer layer. Those 
partly submerged in alcohol and sulphuric acid for the same time 
were wet clear through, the acid having softened the entire mass. 
Alcohol penetrated easily but did not have the disintegrating action 
of the acid. When totally submerged in the above liquids for one 
hour, the acid and alcohol readily entered the proximal end from 
which the moth escapes and also penetrated the sides, but water 
was effectually kept out, the fringe-like ends of the layers being 
bunched together sufficiently for that purpose, and the pressure 
of the air inside the cocoon undoubtedly helping also. 
It is a generally accepted fact that the interiors of cocoons are 
coated all over with a gummy resinous substance, also that the 
emergence is usually effected by a fluid secreted by the insect, 
which has the property of softening the threads and gum. 
The following paragraphs from Trouvelot explain how this is 
accomplished: 
“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 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 attempt to open the 
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 
