52 BLIND VERTEBRATES AND THEIR EYES. 



(b) The Vitreous Body. --The vitreous cavity is represented by a vertical slit 

 extending from the axis of the eye downward to the edge. The choroid fissure 

 (fig. 18, chr.f.) thus remains permanently open in so far as the edges of the opposite 

 sides of the fissure are not united. A space a few microns wide was found in one 

 eye. In other cases there is no real cavity and no vitreous body. The hyaloid 

 membrane (fig. 18 and fig. 19, hd) is represented by a few cells with elongated nuclei. 

 Blood-vessels were not found in it. 1 



(c) The Lens. — In two specimens no traces of a lens were found, but in 

 two other specimens a lens was present. There being no pupil and no vitreous 

 cavity, the lens is situated in a little depression in the distal face of the retina 

 (figs. 18 b, c, d). The lenses differ greatly from each other. In the better 

 developed instances (fig. 18 b) it is composed of a spherical mass of cells. The 

 nuclei are granular and are surrounded by a hyaline cell body. These little cap- 

 sules are closely packed in a slightly darker matrix. The whole lens is surrounded 

 by a fibrous capsule containing elongated nuclei. Both eyes of one individual are 

 provided with lenses as described. In another individual the 2 lenses differ ma- 

 terially not only from those described, but from each other both in structure and 

 size. The left lens consists of a lenticular nodule containing about 6 dense nuclei 

 (fig. 18 d). On the right side (fig. 18 c) the lens is much larger. It consists of 

 2 large nucleated capsules surrounded by a matrix containing a few dense elon- 

 gated nuclei similar to those of the capsule surrounding it (figs. 18 b, c, and d, are 

 drawn to the same scale). The difference exclusive of size between the 2 lenses 

 c and d and the lens represented in figure 18 b, may be due to differences in the 

 method of preparation. 



(d) The Retina. — The numbers in the following paragraphs are not consecu- 

 tive, but are those used to designate the corresponding layers in the figures. 



(1) The pigment epUhelium forms a complete outer layer of the eye exclusive 

 of its distal face and a narrow strip along the choroid fissure. The extent to which 

 this epithelium is pigmented differs greatly in different eyes. A region along either 

 side of the choroid fissure is free from pigment, occasionally parts of the anterior 

 face of the eye are free from pigment (fig. 19 ft), and very frequently the cells of 

 this layer around the distal margin of the eye are free from pigment. Over the 

 anterior face of the eye this layer is usually composed of a regular layer of cells 

 whether these are free from pigment or not (figs. 19 a, b). On the posterior face the 

 series of cells is not nearly so regular. The pigmented epithelium is here invaginated 

 and folded upon itself in various ways. The infoldings are sometimes solid masses 

 of pigment cells, but sometimes they form hollow spheres which contain a mass 

 of concentrically arranged unpigmented material, probably of choroidal origin 

 (plate 3, f, and text-fig. 19 c.) What the significance of these cysts may be I can 

 not conjecture. Indications of similar structures were seen in the eyes of Amblyopsis. 



The narrow stalk of the pear-shaped eye is usually filled with an irregular 

 jumble of pigment cells. In favorable sections it is seen that these are also the 

 result of an invagination of the pigment epithelium from the pointed end of the eye 

 (fig. 19 b). The pigment epithelium has not been reduced at the same rate as 

 the rest of the retina; as a consequence it is infolded in various ways. Small 



1 The figures were drawn with camera lucida from sections mounted in balsam; 2 mm. objective and 4 eye- 

 piece. The horizontal sections were made from above down and are so drawn that the anterior face of the figure 

 is toward the top of the page. 



