MOLLUSCA. 47 
said to have the same property ; a purple fluid is 
poured out from beneath the mantle, but it is so 
fugitive that no application can prevent its speedily 
turning to a dull rusty colour. 
Colonel Montagu mentions one of our marine 
shell-fish (Scalaria clathrus) as secreting a purple 
juice. ‘‘It may be collected either from the recent 
or dried animal, by opening the part behind the 
head; and as much can be procured from five in- 
dividuals as is sufficient, when mixed with a.few 
SCALARIA. 
drops of spring-water, to cover half a sheet of paper. 
Neither volatile nor fixed alkali materially affects 
it; mineral acids turn it to a bluish green, or sea- 
green; sulphuric acid renders it a shade more in- 
clining to blue; vegetable acids probably do not 
affect it, since cream of tartar did not in the least 
alter it. These colours, laid on paper, were very 
bright, and appeared for some months unchanged 
by the action of the air or the sun; but, being ex- 
posed for a whole summer to the solar rays, in a 
south window, they almost vanished. The appli- 
cation of alkali to the acidulated colour always 
restored it to its primitive shade, and it was as 
readily changed again by mineral acid.” * 
I have already mentioned some thread-spinners 
among the Mollusca; there are others which have 
* Test. Brit. Supp. p. 122. 
