i88 2 .] 
Silks and Silkworms . 
S5 
differing in form. Lastly, these scales are easily detached* 
so that if a moth has struggled on being captured, the scales 
from different parts of its wings become more or less blended, 
and two observers in taking portions for microscopic exam- 
ination can rarely hope to obtain quite identical forms. I 
have compared the author’s figures of the scales of Saturnia 
carpini , male and female, as taken from the middle of the 
anterior margin of the fore wing, with corresponding speci- 
mens from my own collection, and whilst I find the general 
structure of the scales correctly rendered, I fail to recognise 
the well-marked sexual distinction shown in Mr. Wardle’s 
plates. His remark that there is no relation between the 
size of the scales and the size of the inseCt producing them, 
or the extent of its wings, is perfectly correct. The state- 
ment that there is a correspondence between the size of the 
scales in any species and the thickness of its thread, I have 
not had an opportunity of verifying, but it deserves attention. 
Mr. Wardle gives a table of the diameter, strength, and 
tension of the fibre of several of the most important silks. 
There is no mention as to any difference in diameter between 
the thread of the male and the female in any of the species 
examined. An error is exposed which has found its way into 
some entomological works. The two threads which issue 
from the orifices of the silk-glands are sometimes said to be 
twisted round each other as they issue from the so-called 
spinnerets. This is a mistake, as on microscopical examina- 
tion they are found to be simply laid side by side. 
A most important point is the colour of the silk produced 
by each species : that of the common silkworm is generally 
white, sometimes more or less verging to a yellow. In the 
other species the silk is of a deeper colour, verging some- 
times towards a green and sometimes to a brown. Hence 
before the silk can be used in the manufactures, except for 
some especial deep and dark shades, it requires to be 
bleached. Here, accordingly, was the first obstacle to the 
utilisation of the wild silks. The produce of the common 
silkworm is easily bleached, either by the process of “stoving” 
— i.e. f exposure to the fumes of burning sulphur — or by 
steeping in solutions of the bisulphites of soda or of mag- 
nesia, slightly acidulated with hydrochloric or oxalic acid. 
In both these methods sulphurous acid is the aCtive principle, 
and destroys the colouring-matter of the silk by depriving it 
of its oxygen. But this method of bleaching, so satisfactory 
with the silk of the common mulberry-eating silkworms, 
fails altogether with the wild silks. The late eminent tech- 
nical chemist Tessie du Motay, therefore, tried to bleach 
