76 ZOOLOGY. 
These animals are microscopic, glutinous, and translucent, but tinted with 
bluish, reddish, brown, or yellow, the tints being uniform in each species. 
The soft parts are inclosed in a calcareous (rarely cartilaginous) shell, 
fitted to the varied outline of the body, and presenting numerous variations 
in form, affording characters for genera and higher groups. It has one or 
more openings, or numerous pores, which allow egress to certain filaments 
used as organs of locomotion. These can be extended to six times the 
diameter of the body, and they recall the allied organs in the Echinodermata 
and Cirrigrada. They are ramified like the branches of a tree, and have 
the power of secreting calcareous matter upon the outside of the shell, in 
which they resemble the extensions of the mantle in some orders. The 
characteristic name Rhizopoda of authors, has been drawn from these 
filaments. 
The Polythalamia inhabit most seas, and they are so abundant that 
D’Orbigny calculated that an ounce of sand from the Antilles contained 
3,840,000 individuals. The same author informs us that these little beings 
from a sixth to half a millimetre long, are more abundant than the minute 
crustacea, or the infusoria whose shields form the tripoli of commerce. 
Banks are formed by them dangerous to navigation ; they obstruct bays and 
straits, of which the celebrated harbor of Alexandria is an example; and 
with the coralligenous zoophyta they form reefs and islands. 
In a fossil condition they are no less conspicuous. In Russia calcareous 
beds are formed by a single species of Fusulina, and various species enter 
largely into the composition of chalk and certain tertiary formations. They 
are so abundant as in some cases to amount to 3,000,000,000 in a cubic 
metre; and the city of Paris and the surrounding towns are almost built of 
them, so abundant are they in the materials used. Dr. Buckland makes 
the following remarks :.‘‘ Nummulites are so called from their resemblance to 
a piece of money; they vary in size from that of a crown piece [!] to 
microscopic littleness, and occupy an important place in the history of fossil 
shells, on account of the prodigious extent to which they are accumulated 
in the later members of the secondary, and in many of the tertiary strata. 
They are often piled on each other nearly in as close contact as the grains 
in a heap of corn. In this state they form a considerable portion of the 
entire bulk of many extensive mountains, ¢.g. in the tertiary limestones of 
Verona and Monte Bolca, and in secondary strata of the cretaceous forma- 
tion in the Alps, Carpathians, and Pyrenees. Some of the pyramids and 
the sphinx of Egypt are composed of limestone loaded with nummulites. 
It is impossible to see such mountain masses of the remains of a single 
family of shells thus added to the solid materials of the globe, without 
recollecting that each individual shell once held an important place within 
the body of a living animal; and thus recalling our imagination to those 
distant epochs when the waters of the ocean which then covered Europe were 
filled with floating swarms of these extinct molluses, thick as the countless 
myriads of Beroe and Clio borealis that now crowd the waters of the 
polar seas. Lamarck, in his observations on Miliola, remarks that these 
very minute animals have had much more influence on the masses which 
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