Paekke. — Retinal Pigment. 



EXPLANATION OF PLATE. 



All the figures were taken from preparatia 3 of the eyes of Palcemonetes vul- 

 garis Stimp. They were drawn with the aid otm Abbe' camera, and are all mag- 

 nified 335 diameters. 



ABBREVIATIONS. 



Cone cell. fbr. r. Ketinal nerve fibre. 



Distal retinular cell. mb. ba. Basement membrane. 



Proximal retinular cell. nl. con. Nucleus of cone cell. 



Accessory pigment cell. nl. crn. Nucleus of corneal hypodermis cell. 



Cone. nl. px. Nucleus of proximal retinular cell. 



Corneal cuticula. rhb. Rhabdome. 



Longitudinal section of an omraatidium, showing the arrangement of 

 pigment cliaracteristic for the light. 



Longitudinal section of an ommatidium, showing the arrangement of 

 pigment characteristic for tlie dark. 



Transverse section of a cone from an ommatidium, such as is shown in 

 Fig. 2 (dark). 



Transverse section through the proximal processes of the distal retinular 

 cells in an ommatidium such as that shown in Fig. 2 (dark). 



Transverse section through the distal retinular cells of an ommatidium 

 such as that shown in Fig. 1 (light). 



Transverse section through the retinula (rhabdome and proximal retinular 

 cells) of an ommatidium like that shown in Fig. 1 (light). 



Transverse section tlirough two groups of retinal nerve fibres. 



Lateral view of a cone with one of its two distal retinular cells still 

 attached. The distal retinular cell shows the condition characteristic 

 for the dark. The preparation was isolated from a retina macerated 

 in Midler's fluid. 

 Fig. 9. Longitudinal section through the bodies of two distal retinular cells, 

 which show slight foldings accompanying their shortening. Tiie 

 preparation was made from an animal which had been kept in the 

 dark thirty-eight days and then exposed to light for four hours and 

 three quarters. The figure was drawn from preparations made by 

 Professor F. H. Herrick, who kindly granted the author the privilege 

 of studying them and making drawings from them. 

 Fig. 10. Longitudinal section through the edges of two distal retinular cells (see 

 p. 287), from the same set of sections as that from which Fig. 9 was 

 drawn. 



