INFUSORIA. 15 



to Elirenberg an extensive series of novel and extraordinary 

 microscopic organisms, composed of silica, but foraminated 

 like the shells of the Ehizopods. The same forms, and others 

 similar to them, have been met with in the deep-sea mud of 

 the Gulf of the Erebus and Terror, and more recently in the 

 mud of the North Atlantic soundings. They are quite dis- 

 tinct in form and character from most of the silicious-shielded 

 Diatomacece, but some of them resemble the Coscinodiscus and 

 Actinocyclus. No less than 282 forms, grouped in 44 provi- 

 sional genera, have been described. 



Class III. — Infusoria* 



(Polygastria, Ehrenberg.) 



Numerous genera and multitudes of so-called species of 

 free and locomotive microscopic organisms, which, because 

 they do not present the distinctive characters of plants or 

 animals, have been by turns referred to one or other kingdom, 

 possess shells of flint, and consequently enter largely into the 

 domain of fossil evidences of former life. The silicious shells 

 of Infusoria, though not chambered or foraminated, present 

 under the microscope definite and beautiful characters of 

 form and sculpture, as recognisable and distinctive as those 

 of the calcareous shells of Mollusca. The plates of the incom- 

 parable works and memoirs of Ehrenberg abound with exact 

 figures of the delicate sheaths, shells, and shields of the lori- 

 cated Infusoria of past and present seras of life, the deposits 

 of which, by reason of their pure, flinty, atomic constitution, 

 were known in the arts long before science had detected their 

 nature and vital origin. In 1836 portions of the stone called 

 "tripoli" or " polierschiefer" (polishing -slate of lapidaries) 



* These animalcules are readily obtained from infusions of organic matters 

 in water. 



