366 Dr. Wallace on the Oak-feeding 
of clear liquid, and then folding up in its long diameter a large 
leaf, or uniting two or three smaller ones together to keep itself 
concealed, it spins a network of coarse silk like the Cynthia, at- 
taches it to the bough with a short rope formed of several strands 
flattened, and then commences in earnest the more serious business 
of its cocoon, 
The cocoon of Bombyx Yamamai most closely resembles that 
of B. Mori; the resemblance is often complete, except in point 
of size; like it the shape is oval, it is closed at both ends, the 
colour is greenish or golden yellow. It is much larger than that 
of B. Mori; it measures in its largest diameter 14 to 24), inches, 
in thickness 7%, to 1,4, inch. The largest are generally those of 
the females, but some very fine cocoons have produced enor- 
mous males. The worm commences to spin around hima web at 
first transparent, but which soon thickens in proportion as the 
new meshes are stretched across those first spun. The thread, 
nearly always continuous throughout the cocoon, measures in 
length from 870 to 1,100 yards. In the external layers the thread 
is carried nearly round the cocoon, but in the internal ones circles 
are formed more or less numerous, first at one end and then at the 
other. By this arrangement the worm works more freely and 
rapidly, and the moth makes its exit more easily, as the threads 
which it detaches easily pull out, lengthen and stretch, facilitating 
thereby the passage of the insect. Externally the silk is of a 
deep green or yellow colour, but internally of a silvery whiteness ; 
the inside is also finer and more brilliant. As with all silk-produc- 
ing species the fibre is composed of a double thread, for the reason 
that there are two orifices (spinnerets) in the larva through which 
the thread is emitted; but there is one peculiarity which renders the 
silk of B. Yamamai very superior, viz. :—that as is the case with 
B. Mori, the fibre is covered with a gummy material, which is not 
perfectly dissolved in the boiling water which contains the cocoons 
during reeling, so that the two or more threads become during the 
process as it were naturally agglutinated together and compose a 
single strand. The cocoon throughout is strengthened with a 
thick gum, but this softens readily in boiling water; this gum 
seems to contain a calcareous element, for on drying the cocoon, 
and rubbing or tearing it, a whitish powder tumbles out, which is 
often distinctly visible on the surface of the cocoon. The larva 
continues spinning during four or five days, little by little shrink- 
ing up in his narrow prison ; afterwards he remains motionless for 
five or six days, after which a new moulting occurs, and the worm 
is changed into a pupa. 
