POLYPI. RADIATA. ESCHARA. 351 



active in their motions, constantly protruding themselves from 

 their bell-shaped recesses, and very suddenly retreating. 



MeMBRANi'pORA PILO'sA, Johnston; LVir Zoo/;/;., 280, pi. 24, f. 10- 

 12. Farre ; Philos. Trans., 1837, pi. 27, f. 1 - 5. Flustra pilosa, Lin. 



Encrusts small sea-weeds and old shells with a membranous 

 lace-work, from each of the meshes of which a hair is seen to is- 

 sue, unless worn off by friction, as it usually is. 



AlcYO'NIUM ECHINa'tUM, Flem. ; Brit. Anim., 517. Johnston ; 

 Brit. Zooph., 3U4, pi. 42, f. 3, 4. 



Of a fleshy nature, encrusting dead univalve shells. It becomes 

 stiff when dry, and is then studded with prickles. Such shells 

 appear enveloped in a greenish, filmy scum. Very common on 

 Buccinum unddtum. 



EsCHA^RA FOLIA'CEA, Lam. Johnst. ; BWt. Zoo/)A., 297, pi. 40. Milne- 

 Edw.; .inn. des Sc. J^at., vi. 36, pi. 3, f. 1. 



Drawn up from deep water. It is a broad membrane, less than 

 a tenth of an inch in thickness, gathered into a flounce. It is so 

 light as to float in water, becomes crisp when dry, of a yellowish- 

 brown color, and is punctured with numerous pores on both sides. 



The Corallines and Sponges have by many been ranked 

 among the Polypi. But recent observations have proved that 

 neither of them are inhabited by polypi. 



The Corallines are now fully proved to be of a vegetable 

 character, allied to the Algae. We have at least one species, 

 which we find attached to shells which are rolled up from the 

 deep, and also along rocky shores, growing in the little basins 

 which are filled by the dashing of the surf into them. It is of a 

 brownish color when living, but soon becomes white on exposure 

 to the air, and is probably CoraUina rubens of Linnasus. 



The Sponges still hold a disputed ground between animals and 

 vegetables. Their claim to a place in the animal kingdom seems 

 to rest on the power which the ovules or young are observed to 

 have of floating from place to place at will, by means of vibratory 

 ciliae. When they have once attached themselves to some solid 

 body, as they always do, they do not afterwards manifest any in- 

 dications of sensation or volition. 



