CONTRIBUTIONS TO THE BIOLOGY OF THE GREAT LAKES. 
ROTATORIA OF THE UNITED STATES. 
II. A MONOGRAPH OF THE RATTUEI DAE. 
By H. S. JENNINGS, 
Assistant Professor of Zoology in the University of Michigan. 
INTRODUCTION. 
There is perhaps no need so great in American zoology as to have the different 
groups of invertebrates thoroughly described and set in order, so that the worker in 
ecology, physiology, variation, or morphology can determine them without becoming 
a professional systematist. As matters stand at the present time, most of our 
aquatic invertebrates can not be determined without the study of much scattered 
literature, ancient and modern, and much wearisome and unprofitable sifting of 
synonymy. 
Happily there is at present a strong movement toward remedying this state of 
affairs. AVhat is needed is a set of studies comprising monographic treatments 
of the various groups — each account of a group complete in itself, so far as the 
American species are concerned, so that any species of the group can be determined 
without reference to other literature. This can be accomplished if different inves- 
tigators select circumscribed groups of not too great extent, perhaps a single genus, 
and set this thoroughly in order, describing and figuring all species likely to occur 
in America, and bringing the names into consonance with recognized rules of 
nomenclature. It is such a study of one of the families of the Rotatoria that is 
herewith presented. 
The Battulidce are a family of free-swimming Rotatoria, containing altogether 
about TO to T5 species. Their chief general interest lies in their peculiar u asym- 
metrical structure, most of them having the organs so disposed as to give the impres- 
sion that the body has been twisted, while the primitive bilateral symmetry is still 
further disturbed by a number of the organs becoming rudimentary on one side. 
They are found as a rule amid aquatic plants in the quiet parts of lakes, ponds, 
and streams. Only one of them ( Rattulus capucinvs Wierz. & Zach.) can be said 
to be limnetic — that is, commonly found free-swimming at a distance from the vege- 
tation of the shores and bottoms. A few occur in swamps; but clear water, amid 
actively growing vegetation, is the place where the Rattulidce ■ abound. In such 
regions they are often among the most abundant of the Rotifera. 
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