Observations on the structure and nature of flustrae [Part 2] / by R. E. Grant.

Date:
[1827]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the structure and nature of flustrae [Part 2] / by R. E. Grant. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    sometimes observe parts, in other calcareous zoophytes, possessing distinct power of motion, though apparently unconnected with the body of the polypi; thus in the Cellaria avicidaria, Lam. whose polypi have the same structure, and the same connection with the cells as in jiustrce, I have observed in living specimens a constant motion of flexion and extension in the remarkable testaceous processes shaped like a bird’s head, and attached by pe- duncles to the outside of all the cells. These processes or organs are likewise provided with lateral folds, like the valves of a shell, which have a distinct and regular motion corresponding with the flexion and extension of the entire process. The aper- ture of each cell of the F. foliacea, is defended by four project- ing spines, which arise from the calcareous margin of the cell. There are two spines on each side of the aperture, and the upper two are more than twice the length of the lower pair, and slight- ly curved upwards. When we look transversely on the surface of a branch, the spines appear to be arranged in very regular transverse curved rows, and when we observe the surface longi- tudinally, they appear to be arranged in very regular longi- tudinal straight lines. The spines are calcareous, tubular, cylindrical, shut at their extremity, and appear obviously destin- ed to protect the expanded polypi. The two pairs of spines belonging to each cell are placed only on the upper half of the cell, although, from the contiguity of the cells, the lower half of each is likewise defended by the spines of the adjacent cells, 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. foliacea arc about twice as long as