SYNOPSES OF NORTH-AMERICAN 
INVERTEBRATES. 
XVII. Tue RorATORiA. 
H. S. JENNINGS. 
Tue Rotatoria, or wheel animalcules, consist of minute, 
chiefly microscopic animals, which are everywhere abundant in 
fresh water. Along with the Protozoa they constitute by far 
the largest number of species and individuals among the ani- 
mals to be found in pools, ponds, rivers, and lakes. A few are 
found in the ocean, but the rotifers are typically fresh-water 
organisms. : 
The most characteristic feature in the organization of the 
Rotatoria is the ciliated area at (or near) the anterior end of 
the body, serving as a locomotor organ or to bring food to the 
mouth. Coupled with the.lack of cilia elsewhere on the body, 
this constitutes a character by which a rotifer may as a rule be 
recognized at once. This ciliated area is usually known as the 
corona. It varies excessively in form and structure, and in a 
few rare aberrant species is lacking. 
Male and female differ in form, the males being, as a rule, 
much smaller than the females, and reduced in structure, — 
usually lacking the alimentary canal. The males are little 
known, many species existing in which they have never been 
Observed. Discussions of the structure and classification of the 
rotifers are therefore based generally on the females alone. 
The form of the body is exceedingly varied in the different 
representatives of the group, — ranging from spherical in Tro- 
chosphzera to the excessively attenuated form of Rotifer neptu- 
nius (Fig. 29) or the spiny, turtle-like form of Polychztus 
(Fig. 111). As a rule, however, the body is somewhat elon- 
gated, and is extended at the posterior end, behind the cloaca, 
to form a long stalk or a tail-like appendage, called the foot. 
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