STTTDIKS IN THE KETINA. 361 



of tlie middle layer run together as amoeboid bodies joined by their processes 

 into a network. This is apparently one of the effects produced by the 

 violence of the fixature, the other being the balling together of the nuclei into 

 small globules of refractive chromatin. 



Fig. 17. — lletinal nuclei of the middle layer showing connecting filaments. 

 a. Stickleback (Lindsay Johnson's fluid), b and c. Plaice (Perrenyi) showing 

 stages in the contraction of the chromatin within the nuclei, d. Mouse 

 (? Perrenyi). e. Prog (osmic vapour). 



Pig. 18. — From Amphibian retinas showing the nuclei joined together, the 

 connecting filaments made visible by clumps and coatings of staining matter. 

 a. Prom a tadpole from Table Mountain, fixed 2 a.m., four nuclei, three in the 

 middle layer and one a rod-nucleus ; with two masses, one very large, of 

 extra-nuclear chromatin ; the large mass seems half arrested by the outer 

 reticular layer [p. r. /.). 0. From the same, shows the nuclei of middle and 

 outermost layers not only connected inter se, but the nuclei of the one layer 

 connected with those of the other through the outer reticular layer ; one large 

 mass of extra-nuclear chromatin. Such masses are common, and have, in the 

 human retina, been mistaken for small nuclei, c. Prom a toad tadpole fixed 

 at 2 a.m., with small irregular clumps of extra-nuclear chromatin massed on 

 the filaments, d. Prom a frog tadpole fixed 10 p.m., showing a nearly com- 

 plete nuclear connection from the inner reticular layer on to the rods. 



Fig. 19. — From the retina of a plaice, six inches (Plemminp), from same 

 eye as Pig. 17 b, c. Two nuclei very highly magnified within the outer 

 reticular layer on their way to become rod-nuclei; they send filaments towards 

 the nuclei of both middle and outer layers. 



Fig. 20. — Prom the retina of — a, cat, two days old (Perrenyi) ; b, cat, six 

 weeks old (Plemming), showing the gradual lineal arrangement of the clumps 

 of chromatin ; c, d, old cat, thirteen years (Perrenyi), c showing the filaments 

 connecting the chromatin clumps, and d, the gradual change in the arrange- 

 ment of the chromatin as a nucleus passes through the outer reticular layer, 

 0. ?•./., to become a rod-nucleus; e,f, rod-nuclei of mouse ; y, fatigued and 

 with loss of chromatin. 



Fig. 21. — Prom a human retina. Rods showing in a a specially clear con- 

 nection between the filaments striating the rods and the intra-nuclfar reti- 

 culum. In b bundles of fibrils come down from the upper tiers of the nuclei. 

 « is a rod wilh a swollen inner limb, usually called a cone, but probably 

 having no morphological significance. 



Pig. 22. — A diagram showing how the primitive nerve-fibrillse reach the 

 rods through the intermediary of the retinal protomitomic system ; for further 

 details see text, p. 326. See also p. 339 for the meaning of the asterisk. 



Pig. 23. — From the retina of a frog tadpole (eye diameter 4< mm.) fixed in 

 Pcrrenyi's fluid at 12 midnight. Selected groups {a, b, c) of elements near 



