THE LENS. 2G9 



field of view is strewed with large, clear, rod-shaped struc- 

 tures, some straight, but many of them bent and curved in 

 different directions, and exhibiting a distinct transverse 

 striation, or even a tendency to split up into a number of 

 superimposed disks, this tendency increasing as the pre- 

 paration is longer made. Some of them have what looks 

 like a small appendage jointed on at one end, but this is 

 really the comparatively small inner segment of the rod. 

 The cones are also very small in comparison, and on that 

 account may at first be" missed ; they are distinguished by 

 the possession at the apex of the inner segment of a small, 

 bright, fatty globules, often of a yellow color. Most 

 likely a portion of the hexagonal pigmented epithelium 

 will have come away with the rest of the retina, and in 

 consequence of the rupture of some of the cells the prepa- 

 ration will be strewed with pigment granules which, like 

 all minute granules suspended in fluid, exhibit very strik- 

 ingly the Brownian molecular movement. Some of the 

 pigment cells may be observed intact, either isolated or 

 in patches. If seen in profile, it may be noticed that near 

 one surface (the outer) the cell is almost entirely free from 

 black pigment, while from the other fine streamers of the 

 cell-protoplasm, dotted with pigment granules, extend. 

 In their natural position these pass between and amongst 

 the outer segments of the rods. 



Preparations 31, 32, and 33. The retina of a bird, 

 of a reptile (tortoise), and of a fish are to be teased out 

 fresh in vitreous, in the same way as that of the frog. 

 The chief points of interest in these preparations are the 

 ellipsoid or lenticular bodies in the inner segments of the 

 rods (bird and amphibian) and cones (bird, reptile, and 

 amphibian), the bright, fatty globules of different colors 

 in the inner segments of the cones in the tortoise and 

 bird, and the twin or double cones, especially large in the 

 fish's retina. The various other points in which the retina 

 in these animals differs from that of mammals, may be 

 studied by employing the same methods of preparations 

 as for the mammalian retina. 



THE LENS AND VITREOUS HUMOR. 



Preparations 34. The lens fibres. The fol- 

 lowing will be found the best mode of isolating the 



23* 



