RHIZOPODA. 185 



diminish the numbers of the so-called Infusoria ; many forms have been 

 shown to be only larval worms, while whole genera (as Diatomacise, and 

 Bacillarise) have assumed under the microscope a vegetable character. 

 Siebold distinguishes them from Rhizopods by their having bodies of a 

 definite form, and by moving chiefly by means of vibratile organs, 

 instead of prolongations and digitations of the sarcode. 



Infusoria inhabit both fresh and salt waters, and are all recent, — 

 the fossil organisms often called Infusorial being Foraminifers, Poly- 

 cystic and Diatoms. 



CLASS II.— RHIZOPODA. 



These Protozoans are mostly microscopic, and consist of one or more 

 cells, — the compound kinds takiog fanciful shapes. Each cell is occu- 

 pied by a separate animal or zooid (except in the Orbitolites), though 

 they are organically connected. The animal is of the simplest form 

 possible, having no permanent mouth, stomach or members. It is a 

 gelatinous, fleshy, somewhat granular substance, without appreciable 

 organization. From this body are thrown out at will long, delicate, con- 

 tractile filaments, resembling roots (whence the name Rhizopod), which 

 are used like the tentacles of the Polyp for locomotion, and for the in- 

 troduction of food. The majority have the power of secreting a testa- 

 ceous envelope, either siliceous or calcareous; a few are naked; while 

 fewer still are strengthened like the Sponge by spicula. The Class is 

 divided by Carpenter, according to structural characters, into three 

 orders : Lobosa, (as the changeful Amwbse), Radiolaria, (as the silicious- 

 shielded Polycystinise, — best known as the "Fossil Infusoria of Bar- 

 badoes,") and Reticulosa. The Protozoans of the last Order are gener- 

 ally enclosed in calcareous shells, and constitute the interesting group of 

 Foraminifera. The existence of these microzoa was first made known 

 to naturalists by Beccarius nearly 150 years ago. They were first rank- 

 ed as minute forms of Nautili, and even D'Orbigny, in his first memoir 

 (1825), described them as Cephalopods. It was reserved for Dujardin, 

 ten years after, to demonstrate their Rhizopod type of structure. Since 

 then our knowledge has been greatly extended by the elaborate re- 

 searches of Williamson and Carpenter. 



The Foraminifer is a marine animal, dwelling in a shell of extreme 

 beauty, sometimes simple, but usually consisting of an aggregate of 

 chambers which intercommunicate by minute apertures, whence the 

 name. These chambers grow by successive gemmation from a primor- 



