Scientific Intelligence .-—Comparative Anatomy. 421 
of the upper part and sides of the body, is strewed over 
with numberless small coloured grains or vesicles, nearly the 
size of a grain of sand. Even the iris of these mollusca is 
richly ornamented with coloured vesicles, which communicate a 
new beauty to the shining and variegated metallic lustre with 
which it is painted. Each of these vesicles has but a single co- 
lour. The principal colours in the species of cephalopoda, that 
occur in the Mediterranean, are yellow, rose-red, chesnut-brown, 
sky-blue, and of different degrees of intensity. The seat of 
these coloured vesicles is in the mucous substance, and they are 
covered by the epidermis, which is smooth and transparent. 
They have no visible connection with any vascular system, nor 
with the part of the body immediately below them ; they are 
simply animated by very delicate nervous filaments, which are 
scarcely discernible, even by means of a microscope. The co- 
lour with which they are provided is not from a circulating fluid, 
nor from a contained fluid, but belongs to their structure. Our 
author first describes the properties of these vesicles in the dead 
and afterwards in the living animal. 
(1 .) Appearances in the Dead Animal — All these coloured ve- 
sicles exhibit a kind of systole and diastole, or rather a contrac- 
tion and expansion. This motion, in these vesicles, is produced 
when we blow on the animal, or expose it to the light, or touch 
it gently with the finger. During the systole the grains become 
extremely minute, while, during the diastole, they expand to 
fifty times their former size. In this state of expansion, the co- 
loured vesicles assume the form of empty grape-husks. When 
these vesicles, during their diastole, have acquired their great- 
est degree of expansion, they open generally in the middle of 
the upper side, seldom er lower down, when a round hole ap- 
pears. The edge of this opening appears to be surrounded by 
a circular muscle, which is also capable of contraction and ex- 
pansion. 
(2.) Appearances in the Living Animal— l. When the ani- 
mal is in a state of repose, the vesicles are contracted, and 
are not visible. 2. When the animal is excited, by being touch- 
ed with the hand, or otherwise irritated, the coloured vesicles 
shew themselves, are instantly in motion, and appear and disap- 
pear with the velocity of lightning ; sometimes like spots, which 
