MOLLUSCA. 45 
rates a diseased condition of the body, deadly to 
other creatures. The Leith mussels, he adds, were 
living in a dock, where we may presume they were 
nurtured and fattened amid putrescent matters; and 
Dr. Coldstream, than whom no one is better quali- 
fied to decide the point, gave it as his opinion that 
the liver was larger, darker, and more brittle than 
in the wholesome fish, and satisfied Dr. Christison 
that there was a difference of the kind. It must 
be confessed, however, that these observations leave 
the question pretty nearly where 1t was before. 
Some peculiar secretions of the Mollusca remain 
to be noticed. And first the black liquor or ink of 
the Cuttles and Squids, which has already been 
mentioned as useful to man, but which is doubtless 
much more useful to the animals themselves. These 
animals, when in danger, are known to pour forth 
from a funnel-like orifice a liquor of a blackish- 
brown colour in considerable abundance ; this fluid, 
readily diffusing itself and mingling with the sur- 
rounding water, produces such a cloud of obscurity 
as frequently enables the crafty animal to escape, 
enveloped in the mist of its own making,—as the 
deities in Homer are represented as concealing 
their favourite heroes. 
Somewhat analogous to this is a secretion of a 
rich purple hue produced and poured forth under 
excitement, by those large and naked mollusks, the 
Aplysiec. I have found one of these animals, on 
being put into a vessel of clean sea-water, change 
the whole to a brilliant purple in a very few 
minutes; and on the water being renewed even 
again and again, produce the same result. This 
was a West Indian species, but there is one found 
occasionally upon our own coasts which has the 
