MISCELLANEOUS. 73 



der the place of many zoophytes provisional, more especially such as are 

 of recent occurrence. 



The present subject is diffused as a single stratum, for the most part 

 investing the leaves of the Laminaria digitata, or common tangle. 



It may be easily recognised by its whitish colour, and stellate form, 

 extending by irregular prolongations, which terminate in some orginating 

 cells. Specimens are of very various dimensions, from a small spot to a 

 considerable superficial area, equalling several square inches. — PI. XXIII. 

 fig. 1. 



This zoophyte spreads its single stratum of cells over the leaf, under 

 slight modifications of form, sometimes oblong, and with curving sides. 



The cell itself, when apparently in greatest perfection, tends to an 

 elliptical shape, and is guarded by six marginal spines ; the whole, how- 

 ever, are not peculiar to each single cell, but are set on the margin or par- 

 tition common to two cells. The figure of the cell may be more liable to 

 modification, according to the difference of specimens. — Figs. 2, 3. 



They are partially covered by each other in their respective rows. 



An ascidian hydra of such transparence as to be indistinctly seen 

 when stretching over the others, is the occupant of the cell. It is the 

 posterior portion of the body which is covered by the cell behind. No- 

 thing peculiar distinguishes the hydrse from the ordinary nature of their 

 race, figs. 4, 5. But I have had considerable difficulty in obtaining them 

 alive, fig. 6. On contamination of the water many drop from their cells. 



The increment of the product seems to be effected by an embryo ad- 

 vancing between two perfect cells with their hydra. 1 . Thus the central 

 cell between two in maturity with their hydrse displayed, is advancing at 

 the upper extremity of fig. 7. 



The naturalist should be warned that the noxious principle speedily 

 imparted to sea- water by the Laminaria digitata, though seeming in the 

 freshest condition, becomes fatal to all zoophytes within its influence. 



Plate XXIII. Fig. 1. Flustm membranacea on a leaf. 



2. Perfect cells. 



3. Cells of modified form. 



VOL. II. K 



