Parker. — Lobster E^e. 



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

 cessory pigment-cells of each ommatidiuni arc apparently separated 

 by an intervening space from those of neighboring ommatidia. Tiiis 

 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 retinula; 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. Tartially depigmented. 



The pro.ximal tip of the rhabdome. Completely depigmented. 



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

 pigmented. 



A diagram of Fig. 10. The proximal retinula' of the different ommatidia 

 have been numbered to correspond with those of ommatidium c in 

 Fig. 15. Tlie retmula; of ommatidium '• are tinted pink. 



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

 membrane. Tlie Hue n z shows tlie plane of section for Fig. 2it; x 

 indicates the cross-shaped thickening in tlie basement membrane. 

 Completely depigmented and stained in Weigert's hajmatoxylin. 

 (See page 4.) x 575. 

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

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

 were taken are as foHows : — 



22. Directly below the basement membrane. Tlie fibres are in groups of 

 threes and fours. 



23. At one fourtli the distance from the basement membrane to the optic 

 ganglion. 



24. At half the distance between the membrane and ganglion. 



25. At the surface of the ganglion. 



14. 

 15. 



10. 



17. 

 18. 

 19. 



20. 



21. 



ABBREVIATIONS. 



mh. i cpt. Intercepting membrane. 

 7nb. i cl. Intercellular membrane. 



luh. pi ph. Peripheral membrane. 

 n.fhr. 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. 



111. con. 

 ill. cm. 

 ill. dst. 

 id. pi'j. 

 nl. px. 

 oiiim'. 

 pi(j. dst. 

 pig. px. 

 r. 



r/ib. 

 rill', dst. 



rtn'. px. 



spa. I cl. Intercellular space of retina. 



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

 tion of the figures with which they are found. 



