STUDIES IN THE RETINA. 73 



early vesicular stage, tlie large vesicles not destroyed by the reagents. The 

 exact relations of the nuclei cannot be made out. The nuclei of the two 

 youngest vesicles may, perhaps, be those shown in or on the outer reticular 

 layer. 



Fig. 13. — A few elements from the same, selected to show some of the 

 form-changes from vesicles to rods. Most remarkable are the " cones " shown 

 on the left («, i, c). Their tips are quite clearly within vesicles. The pheno- 

 menon is explained in the next figure (14). The rod on the extreme right 

 shows one of the bright staining globules referred to in Part II. 



Fig. 14. — A diagram to ex;plain the " cones" shown in Figs. 13 and 15, in 

 which their tips are thrust into terminal vesicles. The pressure of new pro- 

 trusions acting in the direction of the arrows converts the vesicle a into b 

 and c with a progressively lengthening neck. The staining matter which 

 accumulates in tin's neck (see the central element in Fig. 12) is then thrust 

 outwards (1) by the outward movement of the nucleus, and (2) by a fresh 

 discharge of material {d). Tliese " cone " tips, therefore, have no other 

 membrane than the vesicle into which they are thrust. They are therefore 

 sometimes disintegrated, and without defined outline. 



Fig. 15. — Frog tadpole (Perenyi). Eye diameter 0-4 mm. Still shorter 

 and stouter elements showing the same phenomenon, taken at different dis- 

 tances from the centre of the retina. The formation of short thick rods out 

 of vesicles can be easily understood. 



Fig. 16. — From the retina of a frog tadpole (picro-sulphuric, safranin). Eye 

 diameter 0'24 mm., showing early protrusion of vesicles against the pigment. 

 Deeply staining yolk granules are shown here and there; they are left out of 

 Figs. 5 and 6. Two nuclei are shown in the figure not yet in contact with the 

 membrana limitans externa. They are selected because they show vacuoles 

 inside. Intra-nuclear vacuoles and vacuoles extruded within the retina may be 

 seen in all the sections of young eyes ; the earliest phase of the inner reticular 

 layer looks, indeed, like an aggregation of such intra-retinal vacuoles (cf. Fig. 7). 



Figs. 17 aud 18. — From the retina of another frog tadpole of about the same 

 size (from 0*20 mm. to 0*25 mm.). Portions of sections differently magnified, 

 showing more vigorous protrusion of vesicles against the pigment. Those 

 quite in the pigment are often yellowish in colour, while those nearest to the 

 nuclei are clear white, partially framed round with densely staining matter 

 (iron-hsematoxylin). In Fig. 18 the vesicles marked with asterisks were 

 yellowish. In other slides the yellow fluid, which here appeared in vesicles, 

 vras certainly inside the pigment cells as well (cf. Fig. 4). 



Fig. 19. — Frog tadpole (Perenyi). Eye diameter O'S mm.; a group of 

 nuclei crowded outwards. The membrana limitans externa was not distinguish- 

 able ; its probable position is indicated by the marks of interrogation. Where the 

 crowding was seen, the nuclei of the middle nuclear layer was diminished from 



