OYSTERS AND SCALLOPS. 229 
and minutely to every irregularity of its surface. 
“ The shelly case of the Oyster,” observes Sir 
Anthony Carlisle in his eloquent oration, “ is its 
sole security, and a superior delicacy of touch, 
diffused over the whole of the living surfaces, 
warns the creature of every danger, and bids the 
closing of senseless valves. The inward organi- 
zation is equally simple with the exterior forms, 
and both are suited to a passive life; for locomo- 
tive beings demand evidences of distant things,— 
sometimes to supply their wants, and on other 
occasions to inform them of danger; but a sta- 
tionary creature, being doomed to rely on its fixed 
resources, would only be tantalised by evidences 
placed beyond its control.” * 
In the Pectens, the edges of the mantle are 
furnished with eyes and tentacles; the Limes have 
the latter greatly developed, but the former organs 
are wanting, or very minute; the Oysters are 
destitute of both eyes and tentacles. The ap- 
pearance of the eyes of the common Pecten has 
been already described (see p. 5). If we examine — 
one of these organs under a microscope, say with 
a power of 220 diameters, we distinctly perceive 
it to be composed of a large globose lens, invested 
in a transparent coat, which is buried for more 
than half its volume in a socket of granular sub- 
stance, and of a yellowish brown colour, having an 
ill-defined circle near its front part, of a blackish 
hue. This last, under continued pressure, bursts, 
and discharges a deep crimson pigment. 
The genera composing this family are very ex- 
tensive, and widely spread; particularly in the 
seas of warm and temperate climates. In general 
* Hunterian Oration, 1826. 
