72 H. M. BERNARD. 



Figs. 5 and 0. — Yvo^ iadpole (picro-sulplmric). Still younger eyes sliowiiif^ 

 earlier stages in the formation of the inner reticular layer as a kind of splitting 

 of the nuclear ranks into two divisions, tiiose forming the larger division 

 crowding outwards against the pigment, leaving a loose, matted, and staining 

 reticulum in the space from which they have moved. In both sections it is 

 noticeable that nuclei in the very centre have even gone from the innermost 

 layer. In Fig. G the cornea (c.) is seen thinning and clearing of pigment over 

 the axis of the eye, and a nuclear division (k.) is seen near the centre of the 

 retina, the two facts together indicating that the eye was only just beginning to 

 function. 



Fig. 7. — Frog tadpole (picro-sulphuric). Eye diameter 0"20 mm. Shows a 

 still younger stage (i.e. smaller, and with larger cavity in the lens). The 

 crowding outwards of the nuclei in the optic axis not yet appreciable ; the 

 beginning of the split among the loosely arranged nuclei is, however, indicated 

 by an accumulation of vacuolar reticulum along the line occupied later by the 

 inner reticular layer; nuclei seem also to be breaking away from the innermost 

 layer, that forming the later so-called " ganglionic cells." A slight curving of the 

 lateral nuclei, like that shown in Fig. 1, is also seen. The yolk granules which 

 obscure the section are not indicated either in this or in the last two figures. 



Fig. 8. — Frog tadpole, from Table Mountain (Perenyi). Eye diameter 

 O'S mm. ; cross-sections of rods showing deeply stained internal reticulum ; 

 this changes its pattern when the focus is changed. Tiie reticulum is some- 

 times forced to the sides by a refractive greyish mass, which at times may 

 have a brownish centre of the same colour as the pigment. In these cases 

 the reticulum frequently con)es again into view on changing the focus. 



Fig. 9. — From the same retina, showing the distal ends of the cones as 

 vesicles, often torn, but nearly always leaving ragged proximal ends still 

 attached to the conical tips of the staining portion ; in other cases the vesicles 

 are complete, and their distal ends are immersed in pigment ; they are shrunken 

 and often beaded with rows of dots. On comparing the elements marked with 

 an asterisk and numbered 1 to 7, vye can trace the transformation of a cone 

 into a Schwalbe's rod. 



F'ig. 10. — The same, in which the relations are shown more com|)letely. 

 In both these figures the continuation of the vesicle nienibraue into that 

 enveloping the "cone" is quite distinct. On the right is a new element with 

 no staining proximal portion yet visible (cf. Part I, PI. 3, fig. 2, a). 



Fig. 11. — The same, showing the more direct transition of the " cone " into 

 the rod, nearer the side of the retina where tiie elements are shorter (namely, 

 20 n instead of 45 to 50 fi, as they are in F'ig. 10). In this case the distal 

 portion of the cone or new rod was visibly striated, which was not the case on 

 the very young and still slightly swollen Schwalbe's rod shown in Fig. 9 on 

 the extreme right. 



Fig. 12.— From the same retina as Fig. 1. A group of elements in the 



