VARIATIONS IN THE CREST OF DAPHNIA 
HYALINA. 
MINNIE MARIE ENTEMAN. 
THE characteristic tendency of Daphnia to form local varie- 
ties is expressed in D. hyalina by a variability in the cephalic 
crest, such that every kind of crest displayed in the genus 
may be observed in the species, which at the same time 
remains relatively constant in other distinguishing characters 
of D. hyalina. The object of this paper is a comparison between 
the American and the European forms, with a more careful 
. inquiry into the conditions for several lakes offering widely 
different varieties. 
My thanks are due to Professor E. A. Birge, of the Univer- 
sity of Wisconsin, who furnished me with collections from 
northern Michigan and Wisconsin, and through whose kind- 
ness I had access to the literature on the subject; to Professor 
C. B. Davenport, of the University of Chicago, for many help- 
ful suggestions in revising the results of my study ; and to my 
brother, Karl E. Enteman, for assistance while collecting from 
Southeastern Wisconsin. : 
Historical. — D. hyalina was first found by Leydig in the 
depths of the “ Schlier See," and was given its name on 
account of its extremely pellucid character. Following are the 
chief points in its description as given in Leydig’s Natur- 
geschichte der Daphniden, 1860: About as large as D. longi- 
Spina, but somewhat narrowed, and at first sight distinguished 
from all known species by its extreme transparency; the head 
prolonged into a long, straight rostrum, without a ventral 
concavity, and so closely approximated to the thorax that the 
posterior outline is hidden between the valves of the carapace ; 
macula nigra present; terminal claw smooth, showing under 
high power of microscope fine cross striations at base; the 
fornix much higher than in all known forms, the shell delicately 
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