298 ANDREWS. [Vol. V. 



EXPLANATION OF PLATES XX AND XXI. 



All the figures are from camera-lucida drawings made with use of Zeiss lenses, 

 and reduced in reproduction. 1 



Figs. 1-14. Potamilla reniformis. 



Fig. 1. Side view of portion of branchia, preserved, showing one eye by reflected 

 light and filaments in a pigmented area. 2 ■ D. 



Fig. 2. Sensory cell isolated in potassium bichromate and methyl green. 4 • F. 



Fig. 3. Small pigment cells as above. 8 • 4. 



Fig. 4. Sensory cell macerated in H 2 S0 4 sea-water, stained in methyl green and 

 Mayer's acid carmine. 4 • F. 



Fig. 5. A similar cell, not stained. 8 • 4. 



Fig. 6. Separated inclusions of three sensory cells, macerated as above, but 

 cleared in KOH. 4 • F. 



Fig. 7. Longitudinal section of entire eye, showing entrance of nerve and two 

 inclusions. Hematoxylin. 8 • 4. 



Fig. 8. Tangential section near outer surface, showing inclusions and nuclei of 

 pigment cells. 8 • 4. 



Fig. 9. Tangential section through the axial parts of several sensory cells. 8 • 4. 



Fig. 10. Tangential section across the nuclei of several sensory cells. 8 • 4. 



Fig. 11. Transverse section of depigmented eye. 8-4. 



Fig. 12. Tangential surface near surface of depigmented eye. 8 • 4. 



Fig. 13. Transverse section of lateral epithelial surface of branchia, proximal to 

 eye ; to show the optic nerve. 8 • 4. 



Fig. 14. Transverse section of branchial stem and bases of two filaments, showing 

 one eye cut across, skeleton, blood-vessels, and nerves : the muscles are omitted. 2 • D. 



Figs. 15, 16. Sabella microphthalma. 



Fig. 15. Transverse section of outer part of a branchial stem, showing pigment 

 cells in a cluster. 2 • D. 



Fig. 16. Tangential section of half of a pigment spot, with a few swollen, clear 

 cells. 8 • 4. 



Figs. 17-19. Sabella melanostigma. 



Fig. 17. Transverse section of outer part of a branchial stem, showing a pair 

 of eyes cut across. 2 • D. 



Fig. 18. Part of such a section of an eye enlarged. Three refracting bodies in 

 contact with the cuticle; the axial parts of the sensory cells and large nuclei probably 

 belonging to such cells. 8 • 4. 



Fig. 19. Isolated refracting bodies of sensory cells, showing continuity with the 

 cuticle and adherence to the axial pronuclear portion of the cell in one case. 8 • 4. 



1 Figures on Plate XX multiplied by \, except Fig. 1, that by \. Figures on Plate 

 XXI multiplied by T 8 ^. 



