SEA-MOSS. 



FIG. 184. CELLS OF FLCSTRA (Magnified). 



with spines arranged with 

 great regularity. Should the 

 specimen happen to be alive, 

 it will be seen, on placing it 

 in a glass of sea-water, that 

 every cell is inhabited by a 

 little hungry, active animal, 

 Polype-like in its form, but 

 displaying a much more com- 

 plicated structure. Around 

 its mouth are set numerous 

 long tentacles ; but these are 

 not mere smooth filaments, or 

 petal-like appendages, like 

 those of the true Polypes de- 

 scribed in a former chapter, 

 but they are furnished with 

 innumerable cilia arranged in 

 rows, which being set in rapid 

 vibration at the will of the 

 animal, produce strong and 

 constant currents in the sur- 

 rounding water, all of which 

 converge towards the central 

 mouth. By this wonderful 

 provision two ends are ob- 

 tained : the particles of water are incessantly renewed for the purpose of re- 

 spiration, and by the same means every minute substance, animal or vegetable, 

 that happens to be swimming in the neighbourhood, is dragged by the cease- 

 less whirlpool into the -midst of the ciliated tentacles, and thus brought to the 

 mouth, where such as are fit for prey are seized and swallowed. 



On the very Flustra we have been describing there often exists 

 an example of a parasitic production, belonging to the same class, 

 the structure of which is still more marvellous. 



The Sea-Moss (Bowtrfattkia densa) forms beneath the microscope an object of 

 matchless beauty. This little parasitic Polyzoon (Fig. 185) consists of innumerable 

 Polype-like creatures, each inhabiting an extremely delicate transparent tube ; clusters 

 of these glassy cells arise from a creeping stem, common to the whole group. Examined 

 with a microscope, the tubes m which these minute animals live are found to consist of 

 three portions. The lower part is stiff and horny, though quite pellucid ; towards its 

 upper third, however, it becomes flexible, and at length terminates in a marginal row 

 of delicate horny filaments, united by a web or membrane of exquisite tenuity. Above 

 these filaments the ciliated tentacles expand, and form a sort of funnel, of which the 

 mouth is the apex or centre. Though the tentacles are commonly stiff and motionless 

 when expanded, they are highly sensitive, and on the least alarm are drawn within the 

 tube, the mouth of which is "then closed by the beautiful mechanism above described, 

 the horny filaments that surround it closing over them, as represented in the engraving. 



Many species of these marine Polyzoa are furnished with 

 numerous organs appended to the exterior of the cells, which are 

 of a most remarkable and inexplicable character. These organs 



