Naviculcieca.] INFrSOEIAL ANIMALCULES. 303 



expressed by Kiitzing, and, above all, from the plienomenon of con- 

 jugation. This last, so much insisted on as a proof of their vegetable 

 natui-e, has been already dwelt upon in this volume. 



M. Thuret, in his late essay, expresses himself to the effect that 

 there is no more reason in the favour of the one view than of the 

 other. Schleiden, after describing the siliceous lorica, adds : " Such 

 an artificial and complicated structiu'e among plants has no explana- 

 tion, and is entirely without signification. In all actual plants we 

 find the silica present, in quite a different form, as little separate 

 scales or drops, and distributed throughout the substance of the cell- 

 wall." Professor Bailey's opinion is decidedly in favour of their 

 being animals. (See page 217.) 



In a geological point of view, the members of this great section 

 are the most important of organized beings ; for, although individu- 

 ally invisible, they exist in such countless myriads, that they form 

 strata of great extent, and play a far more important part in building 

 up the earth's crust, than the gigantic Saurians of past ages. The 

 town of Richmond, in the United States, is built upon a stratum 

 twenty feet in thickness, composed almost entirely of the siliceous 

 shells of the Naviculacea. This is not an isolated fact. In Bohemia, 

 at Bilin and -lEgina, deposits of similar origin cover many miles of 

 surface. In Sweden and other countries, shells of vai'ious genera 

 abound. These organisms are found in the Pliocene, Miocene, 

 Eocene, and chalk formations; indeed, even the Oolitic and older 

 sti'ata are not without traces of them; hence, although occupying 

 the lowest place in the animal series, they form an extended base of 

 a triangle, on which man stands at the apex. (See geographical dis- 

 tribution, Sec, page 62.) 



The study of these organisms in connexion with agriculture, has 

 not been much attended to ; so much, however, has been ascertained, 

 as to render its importance undoubted. In Guano manui-e, the 

 presence of shells of Bacilla/ria is not thought to add to its fertilizing 

 qualities, but Dr. Bailey has shown that the gTcat fertility of the 

 rice fields of South Carolina is mainly due to them. 



Liatomacea arc very abundant, both in the sea and in brackish tmd 

 fresh water ; some genera are essentially marine, others peculiarly of 

 fresh water habit. 



