PARAMCGECIUM. 89 
cyst. Under the protection of this cyst the excysted Ameba 
lies dormant. All the active vital processes are suspended 
and are only resumed in more favourable surroundings. 
Such a cyst is termed a hypnocyst. Encysted Amebe are 
doubtless transported from pond to pond by the wind or 
other means. 
Such is the simple structure and life-history of this 
little animal. It may be taken as a type of the Sub- 
kingdom PROTOZOA, for it is a single cell and its 
vital activities are conducted within the limits of this cell. 
It is a type of the phylum GYMNOMYXA (naked jelly), 
for its protoplasm is freely exposed to the surrounding water. 
The whole surface of the body performs the functions of 
ingestion, egestion, sensation, and respiration. Lastly, it is 
a type of the class Ruizopopa, for the protoplasm throws 
out blunt pseudopodia. 
II.—PARAMCECIUM. 
Suxs-KINGDOM PROTOZOA. 
PHYLUM CorTIcaTa. 
Cass CILIATA. 
ORDER HOLOTRICHA. 
Paramcecium caudatum is a minute freshwater 
animal which can be easily distinguished with the naked 
eye. Its body is flexible but has a definite shape. It is 
elongated, cylindrical, and rounded at each end. The 
protoplasm in the interior of the animal is of a semi-fluid 
consistency, like that of Ameba, but the definite shape is 
maintained by a hardened outer part of the protoplasm, 
called the cortex. ‘Vhis cortex should be carefully dis- 
tinguished from the ectoplasm of Ameba, which is but 
slightly differentiated from the endoplasm, and is. too 
mobile to affect the shape of the body. 
The cortex secretes on its outer surface a thin hyaline 
cuticle, which is punctured by numerous minute holes. 
Through these holes the cortical protoplasm protrudes in 
the form of c/a, short vibratile hair-like processes which 
contract forcibly in a definite direction. 
