50 Proceedings of the Boyal Physical Society. 



Fig. 4. Part of a colony of the yellow variety, from Loch Fyne, — natural 

 size. 



Fig. 5. A polype in the retracted condition, — enlarged. 



Fig. 6. The same seen from above, showing the anterior end, — enlarged. 



Fig. 7. Anterior end of another polype not completely retracted, — enlarged. 



Fig. 8. Anterior part of an expanded polype, from the side, — enlarged. 



Fig. 9. Three of the pinnate tentacles dissected off to show their cavities, 

 — enlarged. 



Fig. 10. A single tentacle, with a very small tip, — enlarged. 



Fig. 11. End of a tentacle with no tip, terminating in a pair of pinnae, — 

 enlarged. 



Fig. 12. Dissection of the front part of the body, to show the elevated 

 mouth between the tentacles, — enlarged. 



Fig. 13. Vertical section of the upper part of a retracted polype, such as 

 Fig. 5. Objective — Swift, 1 inch. 



Fig. 14. Transverse section of a poly]3e along A B in Fig. 13. Objective — 

 Swift, 1 inch. 



Fig. 15. Small portion {en.) of last Fig. more highly magnified. Objective 

 — Swift, \ inch. 



Fig. 16. Transverse section of polype along c d in Fig. 13. Objective — 

 Swift, 1 inch. 



Fig. 17. Central part of another section similar to last. Objective — Swift, 

 1 inch. 



Fig. 18. Transverse section of polype along e f in Fig. 13. Objective — 

 Swift, 1 inch. 



Fig. 19. Oblique section of polype along line g h in Fig. 13 (upper edge of 

 Figure corresponds to g, lower to h). Objective — Swift, 1 inch. 



PLATE II. 



Fig. 1. The colourless spicules of a small portion of the young stolon of the 

 yellow variety, Loch Fyne. In their natural positions. Objective— Swift, 

 1 inch. 



Fig. 2. a to I selected spicules from same stolon as last Fig. Objective — 

 Swift, I inch. 



Fig, 3. Shape of the simple spicule, diagrammatic. 



Fig. 4. Small portion of colourless spicule from stolon more higlily mag- 

 nified. Objective— Swift, ^ inch. 



Fig. 5. Mass of red spicules from the body wall in their natural positions. 

 Objective — Swift, \ inch. 



Fig. 6. Some selected red spicules from a young stolon, red variety. Ob- 

 jective — Swift, I inch. 



Fig, 7. The ectoderm and its cuticle from the body wall, surface view. 

 Objective — Zeiss, y\ oil-immersion. 



Fig, 8. The same in profile view. Objective — Zeiss, yV oil-immersion. 



Fig. 9. One of the craspeda, surface view as exposed in dissection. Objec- 

 tive — Swift, 1 inch. 



Fig. 10. Part of a tentacle to show its spicules. Objective — Swift, | inch. 



Fig. 11. Some spicules from a tentacle. Objective — Swift, ^ inch. 



