Parker. — Retinal Pigment of Gammarus. 



EXPLANATION OF THE PLATE. 



All the figures were taken from preparations of the eyes of Gammarus ornatus 

 M.-Edw. They were drawn with the aid of an Abbe' camera, and are magnified 

 570 diameters. 



ABBREVIATIONS. 



cl. cm. Corneal hypodermis. fbr. r. Retinal nerve fibre. 



cl. rtn.' Retinular cell. mb. ba. Basement membrane. 



cl. sn. Accessory pigment cell. nl. rtn.' Nucleus of retinular cell. 



con. 

 cm. 



Cone. nl. sn. Nucleus of accessory pigment cell. 



Corneal cuticula. rhb. Rhabdome. 



Fig. 1. Longitudinal section of an ommatidium, showing the arrangement of pig- 

 ment due to exposure to bright light. 



Fig. 2. Transverse section of a retinula from such a preparation as that shown in 

 Figure 1, and taken near the level marked rhb. in that figure. 



Fig. 3. Longitudinal section of an ommatidium showing the arrangement of pig- 

 ment due to the absence of light. 



Fig. 4. Transverse section of a retinula from such a preparation as that shown in 

 Figure 3, and taken near the level marked rhb. in Figure 1. 



