99 ZOOLOGY. 
is considered ; some of the silicious shields being so small, that, according. 
to Ehrenberg, one hundred millions weigh but a grain. They are found in 
flint, semiopal, bog iron ore, ochre, tripoli (and other polishing minerals 
which owe their action to the shields of silicious species), mountain meal, 
a clay which is eaten in Lapland, and another variety in South America, 
but which probably merely fills the stomach without affording nourishment. 
Sometimes these remains form a stone sufficiently light to float in water, and 
strong enough to be employed in building. In Liineburg and about Berlin, 
the infusorial strata are as much as twenty feet deep and twenty miles in 
extent. Infusorial strata have been discovered by William B. Rogers upon» 
the Rappahannoc river at Stratford cliffs, on the Potomac, and on James 
River below City Point; and in other parts of Virginia. These deposits - 
belong to the miocene formation. | 
The extent of the artificial group Infusoria will probably be much reduced 
as researches are continued. Kttzing has separated the Bacdllarta and 
Diatomeew as Alge, and he considers Gaillonella ferruginea to be a 
conferva. He thinks some of these organisms have both a vegetable and 
an animal nature, and that in such simple forms the distinction between 
animal and vegetable does not exist. 
The observations of Unger, Flotow, Thuret, and OC. Th. Siebold, have 
thrown doubts upon the abe nature of other Infusoria of the genera 
Enchelys, Chlamidomonas, Chilomonas, Cheetoglena, and others. These 
researches seem to show that the spores of Algze are locomotive by means 
of vibrillee, although Unger and Bory would contend that these supposed 
spores are animal in their nature, but convertible into plants. 
Agassiz considers many of the Infusoria to be the larve of worms, &c., 
and he seems disposed to suppress the entire class by distributing its 
members among the other classes of animal and vegetable nature. There 
is reason to believe that supposed species of Leucophra and Diffiugia are 
immature Alcyonelle. Neverthless, it would be premature to give up the 
entire class until a greater number of the more distinct forms are 
ascertained to be larvee, because, whilst we admit that individual species 
may have been described under several distinct names, the number of 
infusorial. species seems too great for the comparatively small number of 
worms, &c., likely to be derived from them. 
The name J/nfusoria is adopted here on account of the heterogeneous 
contents of the division; but if future observation renders it probable that 
the removal of portions wil still leave a distinct group incapable of union 
with other classes, these may take the more appropriate name of Protozoa, 
sometimes applied to the entire group; and its symbol, to extend the views 
of Agassiz, will be a circle. 
Professor J. W. Bayley of the Military Academy, West Point, is the chief 
American authority upon the Infusoria. Most of his papers may be con- 
sulted in the American Journal of Science. 
We now proceed to the consideration of the-species figured in the atlas. 
226 
