155 THE SEA. 



organisms. Some three hundred species of Polycystina 

 have been detected in the Barbadoes strata, chiefly by 

 the investigations of Sir K. Schomburgk. The class 

 differs from the Foraminifera, in the circumstance 

 that the shells are siliceous instead of calcareous ; 

 their forms are even more bizarre, and often possess 

 remarkable elegance and beauty. A prevailing type 

 of form is a sort of dome or cupola, with an apical 

 prolongation of spine, and terminating in three equi- 

 distant spines below ; their walls beautifully fenes- 

 trated with large angular or circular perforations, 

 and, both externally and internally, exquisitely sculp- 

 tured, so that they have been compared with "the 

 finest specimens of the hollow ivory balls carved by 

 the Chinese." 



According to Professor Johann Miiller, who has 

 pursued some investigations on the living Polycystina 

 of the Mediterranean, the sarcode is of an olive colour, 

 which forms pseudopodia, that project through the 

 fenestral apertures ; but which, in a retracted state, 

 occupies only the upper vault of the dome, and is 

 regularly divided into four lobes. This is, at least, 

 the case with some species ; but observations on the 

 trans-European types are still very deficient. These 

 animals seem almost as widely diffused as the Fora- 

 mmifera ; but, from their far greater minuteness, they 

 have not been so generally recognised. 



Important as are the two classes of microscopic 

 beings of which we have been speaking, from their 

 vast numbers, and the office assigned to them in 



