74 H. M. BERNARD. 



four deep to only three (cf. the observation of Borysiekiewitz described in the 

 text, p. 2). 



Pig. 20, — From the viviparous bleiiny (Bles' fluid), a. Section of young 

 retina, showing the early stage, with ordinary cones, Schwalbe's rods, and two 

 adult rods forming a double rod. Note the layer of cells at o.r. and the dark 

 zones in i.r. The nuclei wi.«. were about eight deep. b. From old specimen of 

 same. The rods in two kinds only — (1) double rods with enormous inner limbs 

 (22 II by 14 /*), " giant cones," and (2) Schwalbe's rods. The layer of nuclei at 

 o.r. has disappeared, and most of those from m.n. The i.r, is coarse-meshed, 

 and very few strands run radially through, c. From the same, to show the 

 tiglit packing of the swollen inner limbs, or " giant cones." 



Fig. 21. — Section of the retina of a very large old cod (corrosive sublimate). 

 A " giant cone," with inner limb 42 n by 22 /i, and filled with refractive globules, 

 ("rowds of Schwalbe's rods packed in between the " giant cones." The rod 

 fibres end in terminal conical expansions against the o.r. The nuclei {vi.n.) are 

 nearly all gone, while the m.n. layer itself is choked up with solid sheets of amor- 

 phous, finely granular matter, some of which is seen streaming away in a zigzag 

 through the i.r. The nerve-strands {u.s.) are clotted willi finely granular matter. 



Fig. 22. — a — c. Section of the retina of a small plaice, G" (Flemming), to 

 show three parts of the same section, a being nearest the centre. To illustrate 

 the gradual usinir up of the "ganglionic cells" {gl.) and of the nuclei of the 

 middle layer {m.n.) ; the disappearance of the continuous layer at o.r. (the nuclei 

 of Krause's " Membrana fenestrata "), and the increase in the rows of rod 

 nuclei; the gradual accumulations of granular matter in the m.n., and the 

 swelling of the inner limbs. 



Fig. 23. — a, b. From a very old plaice, a. Radial, b. Tangential, showing 

 the enormous accumulation of amorphous matter, extending in this old fish 

 almost completely round the retina. 



Fig. 1\.—a. Sections of retinas of Loch Leven tiout, ca. 7" to 8"(Perenyi). 

 b. Section of very young trout, var. ? To show the change of the i.r. from 

 caily " Punktsubstanz," with fine zigzag " Miiller's fibres" running radially 

 through it, to the coarse-meshed older condition, and with the threads thickly 

 coated with matter in the outer zone. Similar thickened strands arc seen just 

 within the o.r. 



Fig. 25. — From tadpoles from Table Mountain, and characterised by great 

 abundance of pigment. The inner limbs remain small, and the "Miiller's 

 fibres" rise straight from the walls of the rods. In b.d.e., just above the 

 rod nuclei, are seen the dark-staining bodies which seem to correspond 

 with those seen within the expansions of the " rod fibres "seen at o.r. in some 

 of the foregoing figures, c. g. 20, b ; 22, a, b (cf. text, p. 32). 



Fig. 26. — a, b. From the retina of an old cat (13 years) (Flemming), to show 

 the inner expanded ends of the " Miiller's fibres," containing accumulations 



