MUSEUM OK COMI'AkA'lIVK ZOOLOGY. 01) 



preserved. If the retina In macerated, it is hecauHO the preserving fluid 

 failed to penetrate through th<5 pigment luyer 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 I'J 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 hero 

 distiiiguished. The inner reticular layer does not differ from that 

 found in ordinary eyes. liut with the other layers the case is f)uite 

 different. The nuclei are rnuch 1<;hs closely packed than in other eyes, 

 the intervening spaces being occupied by a few scattered fibres. 'I he 

 nuclei appear to be of two rpiite distinct kinds. One kind {l.ca'cy.) is 

 somewhat larger than the other, stains consideraVjly less deeply, is less 

 refractive, and sliows no trace of a membrane. In the other kind, the 

 nuclei are smaller, c/., dJ, 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 d. ; 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, d. ; at a still deeper focus the appearance is that of a 

 dark ring with a light centre, d." 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 visil)]e, are leucocytes. 



Another interesting exce[itional 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 the 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 



