Eyes of Molluscs and Arthropods. 591 



mass of iuterlaciug fibres, which are less intricate near the inner surface 

 of the retina, where the prolougations of the first two sets of cells form 

 a layer of parallel fibres, directed toward the inner surface of the eye. 



At the periphery of the circular, rod-bearing area, the nuclei of the 

 short retinophorae are situated near the pseudo-membrane in large 

 vesicle-like swellings of the celi, whose narrow and rodless inner ends 

 are surrounded by several large fibres from the inner, gauglionic cells 

 (PI. 29, fig. 3S n. rf.'^). The latter, which elsewhere formed a single 

 row above the rods, on the periphery of the retina become more numerous, 

 and form, near the inner surface, several rows difficult to distinguish 

 from the nuclei of the pseudo-retinophorae. It is worthy of notice that, 

 on the periphery of the retina, there is much less specializatiou of the 

 cells, the retinophorae being smaller, and the inner ganglionic cells 

 larger, than in the middle of the eye. 



There are certaiu points in the anatomy of the retina that may be 

 studied to great ädvantage, by isolating it entire, and, after staining in 

 picro-carmine, examiniug either from above or below (PI. 29, fig. 32). 

 In the former instance, one sees at the edge, first, the superficial, single 

 layer of outer ganglionic cells [d] ; below them are the slender ends of 

 the retinophorae, with the inner ring of their large, deeply stained nuclei, 

 and the outer ring of vesicles containing the faintly stained ones [e] ; the 

 nerve fibres continuous with the peripheral ends of the retinophorae 

 are seen projecting in groups beyond the edge of the retina. 



Beneath the retinophorae, is a small number of scattered nuclei 

 contained in large spindle-shaped vesicles, filled with a mass of granu- 

 lar protoplasm in the centre of which is a clear space, containing au 

 ovai, sharply stained nucleus [b). These nuclei belong to those cells which 

 form the transitional stages between the retinophorae and the pseudo- 

 retinophorae. Whether the clear space surrounding the nucleus is pro- 

 duced by artificial shrinkage, I cannot say ; it is, however, certain that 

 the space is invariably present, and furnishes a means by which these 

 cells may be easily recognized. Beneath the last layer, is a fourth, 

 formed by numerous, small, sharply stained nuclei belonging to the 

 inner ganglionic cells, and the pseudo-retinophorae. Toward the inner 

 surface, to examine which it is better to turn the retina on the other 

 side, these smaller nuclei begin to assume a circular arrangement, being 

 placed with their flattened sides toward the centre of the retina [a). At the 

 surface, the nuclei bave disappeared, and we bave, instead, a delicate 

 membrane reaching from the edge of the retina to the beginning of the 

 rods, and extending completely round the retina (PI. 29, figs. 32 and 



