Parker. — Lobster Eye. 



Fig. 13. The rhabdome between its distal end and middle. In this section the ac- 

 cessory pigment-cells of each ommatidium are apparently separated 

 by an intervening space from those of neighboring ommatidia. This 

 space is probably the result of shrinkage and subsequent rupture. 



In the same plane as that shown in Fig. 13. Partially depigmented. 



The middle of the rhabdome. The distal retinulae of ommatidium c have 

 been numbered. Completely depigmented. 



The proximal end of the rhabdome. The accessory pigment-cells in this 

 section have probably been ruptured, as in Fig. 13. 



In the same plane as that shown in Fig. 16. Partially depigmented. 



The proximal tip of the rhabdome. Completely depigmented. 



The proximal retinulae close to the basement membrane. Partially de- 

 pigmented. 



A diagram of Fig. 19. The proximal retinulae of the different ommatidia 

 have been numbered to correspond with those of ommatidium c in 

 Fig. 15. The retinulae of ommatidium c are tinted pink. 



Transverse section of nerve-fibres as they pass through the basement 

 membrane. The line y z shows the plane of section for Fig. 29; x 

 indicates the cross-shaped thickening in the basement membrane. 

 Completely depigmented and stained in Weigert's haematoxylin. 

 (See page 4.) x 575. 

 22, 23, 24, and 25 represent transverse sections of the fibres in the optic nerve. 

 "Weigert's haematoxylin. X 575. The planes at which these sections 

 were taken are as follows : — 



Directly below the basement membrane. The fibres are in groups of 

 threes and fours. 



At one fourth the distance from the basement membrane to the optic 

 ganglion. 



At half the distance between the membrane and ganglion. 



At the surface of the ganglion. 



14. 



15. 



10. 



17. 

 18. 

 19. 



20. 



21. 



22. 



23. 



24. 



25. 



ABBREVIATIONS. 



pi ph. Peripheral membrane. 

 Nerve-fibre. 

 Nucleus of cone-cell. 



" corneal hypodermis. 



" distal retinula. 



" accessory pigment-cell. 



" proximal retinula, 



Ommateum. 

 Distal band of pigment. 

 Proximal band of pigment. 

 Retina. 

 Rhabdome. 

 Distal retinula. 

 Proximal retinula. 

 Intercellular space of retina. 



The other abbreviations which occur on the plates are explained m the descrip- 

 tion of the figures with which they are found. 



