340 D Grant on the Structure and Nature of FlustrcB. 



so that they serve also to protract the polypi when in a retract- 

 ed state. No projecting spines of this kind are found in 

 the F, carhasea, and they form the most obvious character 

 of the F.foliacea. The bundles of minute spicula pointing hori- 

 zontally inwards from the margins of the cells in the F. carhasea 

 are not present, nor apparently required in this species. By the 

 aid of the microscope, we perceive the same vascular appearance 

 of the thin membranous covering of the cells as in the F, car^ 

 hasea, the same dark round spot in the center of those cells 

 which have lost their polypi, the same imperfectly formed empty 

 cells along the margins of the branches, and similar rudimentary 

 polypi in the last two or three rows of cells at the free extremi- 

 ties of the branches. 



The polypi of the F. Jbliacea are about twice as long as 

 the cells, have their body coiled up in a spiral turn, and bifur- 

 cated near its lower extremity, and they have the same attach- 

 ment by bundles of soft loose fibres to the aperture and base of 

 the cells, as in the species already described. They have only 

 fourteen tentacula, sometimes thirteen, which are very long, 

 slender, and ciliated on their two lateral margins. The expand- 

 ed tentacula form a bell-shaped cavity, into which there is a con- 

 stant current of water, produced by the incessant rapid vibration 

 of the cilia^ and in the center of this cavity is the circular pro- 

 minent retractile mouth of the polypus. The tentacula remain 

 in this expanded and regular form, when the polypi are found 

 hanging dead from their cells ; and the same is observed in many 

 other zoophytes, which enables us to observe their number and 

 form with more ease through the microscope. The head of the 

 polypus is small, the body comparatively strong, the continuation 

 of the body below the bifurcation very thick, conical, and taper- 

 ing to its posterior termination, the globular appendix of the 

 body, and its tubular cervix, are smaller than in the F. carhasea, 

 and the same opaque matter is found in the cavity of the globu- 

 lar sac. A distinct and constant revolution of particles is seen 

 in the whole of the tube leading from the body of the polypus 

 into the round sac, as if produced by cihse placed within ; there 

 is no pulsation or contraction of the part, nor can we perceive 

 any fluid passing from that cavity into the vessels so extensively 

 ramified on the coats of the cells. A similar continued vibra- 

 tory motion is seen within the mouth in most polypi, which is 



