FLUSTRA. 29 



f'acture, whence it has perhaps been called the Rough Sea-mat. But it is 

 said that the naturalist must beware of confounding this product of our 

 own coast with another zoophyte, passing by the same name, which be- 

 longs to the Mediterranean Sea, and does not correspond in form. 



If the Flustra hispida of Scotland be plunged amidst recent sea 

 water, during genial temperature of the atmosphere, a thin pale blue 

 cloud will be speedily interposed between its dark irregular surface and 

 the spectator's eye. Let the vessel receiving it sustain a shock ; the cloud 

 is instantaneously dispelled, while the brownish fleshy substance remains 

 prominent as before. 



This illusion may be frequently repeated. The semblance of a cloud 

 arose from a multitude of hydroe elicited from the cells, whither they had 

 retreated, now returning to enjoy the freshness of the renovated element. 

 Their numerous pale tentacula in motion over the darker ground pro- 

 duced a misty shade. 



These minute and active beings are so timid, yet at the same time 

 endowed with such caution, that they sink in concealment from appre- 

 hended danger, and then show by their return when they are relieved of 

 alarm. Plate IX. fig. 1. ; specimen : 2. the same enlarged 



From the consistent brownish, gelatinous or fleshy aspect of this pro- 

 duct, some naturalists, with considerable plausibility, call it carnosa. It is 

 united in firm adhesion to the leaf, whereon the outline adopts various 

 forms, regular or irregular. Viewed by a lens, the surface exhibits nume- 

 rous projections, indicating the position of cells inhabited by as many 

 hydra;. Each is beset by five spines, but no distinct and satisfactory in- 

 spection is practicable, unless the object be brought into a very particular 

 position. — Figs. 3, 4. 



The rough, dark surface of the Flustra remains undisturbed until 

 the summit of the cell projects, to announce the approaching evolution of 

 the hydra. First, a very short white cylinder protrudes, and then the in- 

 tegument of the body, unfolding like the inverted finger of a glove, dis- 

 plays the exterior of the animal, crowned by about 35 tentacula, in cam- 

 panulate arrangement, as if with a reflected lip, formed by their ex- 

 tremities. None of the marine ascidian hydra? have shewn me a eomple- 



