414 MANIPULATION. 



Dictyochalix pumiceus, Pachymatisma Johnstonia, 



Dysidea, Spongilla fluviatilis, 



Geodia Mulleri, laoustris, 



Grantia compressa, Tethea cranium, 



Halichondria panicea, lyncurium. 



Alcyonium. — Nearly allied to sponges is a family of 

 Zoophytes, termed Alcyonidfe, which are often lobed in a 

 pecuhar manner, the outer skin being tough and studded all 

 over with stellate figures, each of which is divided into eight 

 rays ; from these the tentacula of the polypes, also eight in 

 number, may often be seen to issue. The cells for the polypes 

 are situated immediately under the skin, and are the termina- 

 tions of long aquiferous canals, which run through the whole 

 polypidom; the space between the tubes is occupied by a 

 loose, fibrous net-work, the fibres of which, in some places, 

 are more crowded than in others, and there form small com- 

 partments. All the interspaces are filled up with a transpa- 

 rent gelatine, in which numerous irregular spicula lie 

 immersed. These spicula are calcareous, and are mostly in 

 the form of a cross, and toothed on the sides.* They may be 

 obtained from thin slices by maceration, or by burning a small 

 portion of the animal in a spirit lamp, or more simply 

 by boiling the 'gelatinous matter in caustic potash. Three 

 kinds found on the British coasts are admirably described in 

 the work just quoted; these wiU aU exhibit remarkable 

 spicula, and are named as follows : — 



Alcyonium digitatum, A. glomeratum, Sarcodictyon catenata. 



Many other kinds are met with on foreign shores, in which 

 spicula of very peculiar shapes are abundant ; the author has 

 in his possession some sea-sand from Java, of which full one- 

 third of the bulk is composed of the spicula of different species 

 of Alcyonium, Gorgonia, and sponges, and one-third of the 

 remainder of foraminiferous shells. 



• A History of British Zoophytes, by G. Johnston, M.D., LL.D. Lon- 

 don, 1847. 



