V. 
NOTES ON AMERICAN ROTIFERS. 
BY C. L. HERRICK. . 
\Plates II — IV^ and Plate H.] 
Introduction . — -In the series of papers here begun, it is expected to 
treat the subject in somewhat the following order : First, in an intro- 
ductory section, an outline of the general characteristics will be given, 
then we shall proceed to a description of species without attempting to 
treat them in systematic order, finally, if permitted, space may be de- 
voted to a review of the classification and a more detailed discussion 
of anatomy and development. The present installment attempts 
simply to describe a few of the common species of a number of 
genera. 
A rotifer may be described as a worm-like, bilateral, metazoan, 
moving by means of a circum-oral trochal disc, and either adherent or 
free-swimming. Many of the animals of this group are exceedingly 
small and are greatly exceeded in size by certain Infusoria, and it was 
this circumstance, as well as a certain outward similarity in appearance, 
which led Ehrenberg to include both under the one head and to as- 
cribe to Infusoria the same complicated structure he was able to make 
out in rotifers. Living in all fresh waters, these animals are among 
the most accessible objects for the microscope, yet, on account of the 
care necessary in their study and the scattered literature, they have 
been much neglected in America. 
The body of all rotifers exhibits a tendency to segmentation, which 
is, however, mainly confined to the integument. The inner organs 
are but slightly affected by the jointing, except the muscular system 
which is, moreover, largely responsible for the number and arrange- 
ment of the segments. Very generally the body terminates posteri- 
