POLYCYSTINA. 383 
or root-footed animalcules, that form the lowest order of the 
Protozoa, the lowest class of the animal world. ~ 
It is a peculiar feature of these beautiful little shells (whose 
delicate sculpture frequently reminds the observer of the finest 
specimens of the hollow ivory balls carved by the Chinese) that 
they are usually surmounted by a number of spine-like pro- 
jections, very frequently having a radiate disposition. Some 
have an oblong shape (Podocyrtis), others a discoid form (Ha- 
90° 
G09 
Polycystina. 
a. Podocyrtis Schomburgkit. b. Haliomma Humboldtit. 
liomma), from the circumference of which the silicious spines 
project at regular intervals, so as to give them a star-like aspect. 
They are generally of a smaller size than even the Foraminifera, 
appear to be almost as widely diffused, and have also largely 
contributed to the structure of the earth-rind. They were first 
discovered by Professor Ehrenberg at Cuxhaven, on the North 
Sea; they were afterwards found by him in collections made in 
the antarctic seas, and have been brought up by the sounding 
lead from the bottom of the Atlantic at depths of from 1,000 to 
2,000 fathoms. 
The term Infusoria, which formerly comprised a most 
heterogeneous assemblage of minute plants and animals, is now 
confined to the highest order of the Protozoa, distinguished 
from the Rhizopods by the possession of a mouth and of 
ciliary filaments, whose vibrations serve them both for pro- 
