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 organization is equally simple with the exterior forms, and both are suited to a passive life; for locomotive beings demand evidences of distant things,—sometimes to supply their wants, and on other occasions to inform them of danger; but a stationary 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 appearance 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 substance, 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 extensive, and widely spread; particularly in the seas of warm and temperate climates. In general
- Hunterian Oration, 1826.