SUPPLEMENTARY NOTES. C05 
distinctly see lines that are more distant from one another than 
■j^^ of an inch. In this case the sense of touch is more acute 
than that of sight in the ratio of 8 to 1. Mr. Gardener is also 
able, without the assistance of any instrument, to draw a perfect 
circle or a perfect ellipse, moving his hand on the wrist as a centre. 
P. 296. *' The sewses of Conchifers must be very confined ; and 
indeed there is no good ground for attributing to the generality 
of them any thing beyond a sense of touch and taste. That most 
of them may be conscious of the presence or absence of light is 
possible. " Not having any especial organs for seeing, hearing, 
or smelling," says Sir Anthony Carlisle, speaking of the common 
oyster in his Hunterian Oration (1826), " the creature is limited 
to perceive no other impressions but those of immediate contact ; 
and yet every part of its exterior seems to be sensible to light, 
sounds, odours, and liquid stimulants. It is asserted by fisher- 
men, that oysters, in confined beds, may be seen, if the water is 
clear, to close their shells whenever the shadow of a boat passes 
over them." 
** M. Deshayes goes so far as to say that no especial organ of 
sense can be detected among them, unless, perhaps, those of 
touch and taste ; but we must not forget what have been called 
the eye-specks in the Pecten, to the animal of which Poli gave 
the name of Argus, from the supposed number of its visual organs. 
The pectens are free swimmers, and, from their rapid and desultory 
motions, we have heard them termed the butterflies of the ocean. 
The manner in which these motions are executed, especially on 
the approach of danger, indicates the possession of a sense ana- 
logous, at least, to that of ordinary vision. These eye-specks may 
be seen in the Pecten, placed at short intervals round the thick- 
ened edge of the mantle, on the outworks, as it were, of the 
internal part of the animal fabric. ' As locomotion so vision' is a 
general aphorism not without its particular exception ; for there 
is good reason for believing that Spondylus, which is a fixture in 
its adult state, is furnished with these visual specks." {Penny 
Cyclopcedia, vol. vii. p. 432, et seq. Article Conchifera.) Ehren- 
berg has described the eyes of the Medusa aurita to be in the 
form of minute red points on the circumference of the disk. He 
