SEX DETERMINATION IN DINOPHILUS GYROCILIATUS. 331 
tional care, ifc seems almost impossible to believe that the 
males could have been left behind. It is ou the somewhat 
scanty evidence of these instances, and the statements of 
Text-fig. 1. 
Dinophilus gyrociliatus. 
Rudimentary male and full- 
grown female. The female 
shows the broken nature of 
the ciliated bands in the 
head region and the soleno- 
cyte- bearing nepliridia. 
almost the first observation ma 
de Beauchamp (2) that he was 
able to produce partheno- 
genetic development in D. 
conklinii after the exclusion 
of the males, that I have 
based the above statements 
of the occurrence of this con- 
dition. If parthenogenetic 
development does take place, 
then it plays no part in the 
usual life-cycle, but is only 
brought about, as I have 
said, by the artificial exclusion 
of the males under experi- 
mental conditions. Among 
Rotifers, in addition to the 
sexual cycle there is a par- 
thenogenetic one; in each sex- 
determination takesplace,and 
there is no reason, therefore, 
why we should not find the 
same thing* in Dinophilus, 
which all recent morpho- 
logical work has shown to be 
closely related to the Rotifers. 
The present work, from the 
first, was directed along the 
line of studying the influence 
of the sperm on the early 
development of the odgonial 
cells, for the reason that 
e was that of seeing the small 
males actively copulating with the females within the egg- 
capsule, just as these were about to hatch. This is readily 
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