144 bulletin: museum of comparative zoology. 



Szczawinska ('91, p. 536). The transparent axis thus formed is sheathed 

 laterally by five elongated pigment cells, the retinular cells {cl. rtnj). 

 Each retinular cell consists of throe parts : a flattened distal portion 

 applied to the side of the cone ; a middle rod-like portion (Fig. 2, cl. rtnJ) 

 lying against the rabdome ; and an enlarged basal portion proximal to 

 the basement membrane {mb. ba.) and containing the nucleus. The 

 proximal end of this last part becomes attenuated and forms a retinal 

 nerve fibre {fbr. r.) which passes to the optic ganglion. All parts of 

 these cells except the nucleus may contain more or less blackish pig- 

 ment. The space between the ommatidia is filled with a coarse granular 

 pigment, whitish by reflected light and containing nuclei (nl. sn.). This 

 material is made up of the accessory pigment cells, the boundaries of 

 which are not easilv discernible. 



In Szczawinska's description of the eye in Gammarus roeselii, the 

 three parts of the retinular cells described above are stated to be each 

 a separate cell containing its nucleus. She correctly identified the 

 nucleus in the proximal portion. What she believed to be the nuclei of 

 the middle parts (Planche XVI. Fig. 4, n.'^pg.) are without question the 

 nuclei of the accessory pigment cells, which she failed to recognize as 

 such. In the distal portions of the retinular cells of Gammarus ornatus 

 nothing resembling nuclei could be discovered, and I am of opinion that 

 she was mistaken in attributing such bodies to the corresponding parts 

 in G. roeselii. The continuity of the three parts of the retinular cells 

 in G. ornatus can be clearly demonstrated in serial transverse sections, 

 in longitudinal sections, and in isolation preparations, and I therefore 

 believe that these three portions are only parts of one cell. If this is 

 true of G. ornatus, it is probably also true of G. roeselii, and I am 

 strengthened in this belief as Szczawinska's own figures (Planche XVI. 

 Figs. 4, 5) admit more readily of this interpretation than they do of her 

 own. In these respects, then, her account is probably at fault. 



In an eye of G. ornatus that had been subjected to light for some six 

 hours (Fig. 1), a considerable amount of black pigment was found uni- 

 formly distributed through the distal and middle portions of the retinular 

 cells, thus sheathing the cone and rhabdome laterally (Fig. 2). The 

 proximal portion of each cell contained a few irregularly scattered pig- 

 ment granules except near the nucleus, where the pigment was more 

 abundant. 



In an eye from an animal kept some six hours in the dark (Fig. 3), 

 the pigment in the distnl portions of the retinular cells presented the 

 same condition as in the eyes exposed to light. The middle portions, 



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