THE EYE OF PECTEN. 
447 
Avlio have written on this subject. Krohn and Keferstein 
believed it to be spherical. Hensen has figured it filling up 
the space between the cornea and retina, and consequently 
of an irregular bi-convex shape. 
It is difiicult to see how a controversy on such a simple 
subject could have arisen, unless it is because different 
authors have examined different species, and described them 
for the genus. 
x\s regards Pecten maximuSy^n examination of the fresh eye 
has convinced me that in this species the lens is elliptical, the 
major axis being parallel to the plane of the mantle. A section 
of the eye made in a plane at right angles to the plane of the 
mantle and the direction of its margin — that is, the plane 
which is most convenient for section-cutting, and the one 
which is apparently usually adopted — would consequently 
cause the lens to appear circular in section. In the dia- 
grammatic representation of the eye (fig. 1) I have for con- 
venience sake represented the lens as being at right angles 
to the plane of the mantle in order that the true shape of 
the lens may not be overlooked. 
A fresh examination of the lens, when teased out from the 
rest of the eye, exhibits one or two interesting points. The 
lens is not, as in most eyes, perfectly colourless, but possesses 
a well-marked brown colouration, and a number of fine striae 
may be seen running in the direction of the major axis. 
The lens does not appear so perfectly elliptical in the fresh 
condition as in certain sections I have made; it is drawn 
out somewhat longitudinally, so as to be more like a double 
cone than an ellipse. This is probably due to the lens being 
released from the ligaments and connective-tissue pressures, 
which cause it to retain its proper shape. 
Hensen says that the lens is very soft, and the cells are 
light, polygonal, and nucleated. A careful examination 
of the lens of P. maximus has led me to a very different con- 
clusion. The lens seemed to be of exactly the same nature 
as in the higher forms, and when teasing it out I found some 
difficulty in holding it with a needle, as it slipped away from 
under it when a slight pressure was exerted. As regards 
the shape of the cells composing the lens, they are not all 
polygonal, as wmuld be inferred from Hensen^s remarks on 
the subject. In the centre they are polygonal, but as they 
approach the periphery they become more and more flat- 
tened and elongated, until at the periphery they are strap- 
shaped. They are nucleated. As Hensen, 1 could find no 
membrane covering the lens, and no muscular fibres con- 
nected w'ith it; but in a few cases I liave observed a liga- 
