MUSEUM OF COMPARATIVE ZOOLOGY. 69 
preserved. If the retina is macerated, it is because the preserving fluid 
failed to penetrate through the pigment layer in which it is wholly 
incased. Consequently, I shall not dwell at length on the subject, nor 
insist much on the significance of the structure described. Figure 19 is 
a rather highly magnified view of a meridional section of the retina 
near the ora serrata. It will be seen that only the layer of ganglion 
cells, the inner reticular layer, and undifferentiated layer are here 
distinguished. The inner reticular layer does not differ from that 
found in ordinary eyes. But with the other layers the case is quite 
different. The nuclei are much less closely packed than in other eyes, 
the intervening spaces being occupied by a few scattered fibres. The 
nuclei appear to be of two quite distinct kinds. One kind (lewey.) is 
somewhat larger than the other, stains considerably less deeply, is less 
refractive, and shows no trace of a membrane. In the other kind, the 
nuclei are smaller, cl., cl,!, cl.!!, stain deeply, and are refractive in such 
a way that in focusing through them they take on the three different 
appearances shown in the figure; i. e. when seen at a high focus they 
appear uniformly dark, as at cl. ; at a deeper focus the appearance is that 
of a disk with a dark line at. its circumference, a light yellow zone (rep- 
resented in white in the figure) inside of this, and a uniformly dark 
spot in the centre, cl.; at a still deeper focus the appearance is that of a 
dark ring with a light centre, c." A few of these latter have two or 
three longer or shorter processes, but by far the larger number of them 
are spherical, or nearly so. 
No rods are present in these eyes, though this portion of the retina is 
so ragged and formless that it is impossible to say whether they have 
ever been developed or not. It is quite possible that the larger bodies, 
in which, however, no nuclei are visible, are leucocytes. 
Another interesting exceptional case is that presented by the section 
of the eye shown in Figure 12. It will at once be seen that the point 
of chief interest lies in the double layer of pigment that is situated 
behind the lens. within the cavity of the eye. The outermost of these 
layers is in close contact with the posterior surface of the lens, while the 
innermost is in close contact with the inner surface of the retina. I 
cannot, however, satisfy myself that either layer is developed at the ex- 
pense of the parts to which they are respectively adjacent. It is true 
that tho line of contact between the lens and its pigment layer is not a 
sharp one, there evidently being a gradual disappearance of the pigment 
here. The lens, however, shows no flattening on this side, as it would 
were the pigment layer formed at its expense ; but more than this, the 
