46 NATURAL SCIENCE [July 
of males, and he therefore concluded that the ‘resting-eggs’ were 
produced after fertilisation, while the ‘summer-eggs’ (distinguish- 
able by a difference in size into male and female eggs) were partheno- 
genetic. Partly from the fact that very similar phenomena were 
known in other groups, especially in the Cladocera, these views 
obtained general acceptance, despite the fact that in his later papers 
(8) their author found it necessary to point out some difficulties. 
It had already been observed that each individual female produced 
only one variety of eggs, male, female, or ‘resting, during her life- 
time, and Cohn found spermatozoa in the bodies of females which 
were laying male or female ‘summer’ eggs, as well as in those lay- 
ing ‘resting’ eggs. Joliet, in his monograph on JMelicerta (10), 
corroborated these observations, and after giving a careful summary 
of the evidence, suggested that the facts might be explained by sup- 
posing that the sexually produced eggs hatched into females which laid 
‘resting’ egos. In 1885, Plate (12), in connection with his discovery 
of ‘ hypodermic impregnation, arrived at the strange conclusion that 
impregnation was always abortive and without influence on the eggs. 
He contradicted Cohn’s statement that the spermatozoa in the body- 
cavity of the female were attracted to the neighbourhood of the 
ovary, but found, on the contrary, that they disintegrated within a 
few hours after being introduced, without making any progress 
towards reaching the ovary. By observing isolated specimens he 
claimed to show that impregnation was without effect, male, female, 
and resting-eggs being laid indifferently by impregnated and virgin 
females. His explicit statement that he obtained resting-eggs from 
a female isolated from birth is in direct conflict with the results of 
later investigations. Plate concluded that uninterrupted partheno- 
genesis prevailed among the Rotifera, that the males were a vestigial 
and superfluous sex, and that the abortive attempts at impregnation 
were an atavistic phenomenon without present significance in the 
life-history of the species. In 1890, Maupas (16, 17, 19), attacked 
the subject by applying to the rotifers the methods of culture used 
by him in his classical researches on the reproduction of the Infu- 
soria. Unfortunately only very brief accounts of his laborious 
experiments have been published, and many details of his procedure 
are not explained. He found in the species chiefly studied by him 
(Hydatina senta) two varieties of females, distinguished only by the 
eggs which they produced, one kind laying eggs which gave rise to 
females, the other laying only male eggs The females of the latter 
variety alone were capable of being successfully fertilised, and that 
' It would be difficult to find an exact parallel to the curious ‘sub-sexual’ difference 
between these two classes of females. That it is not accompanied by any conspicuous 
difference of size or structure is certain, but it would be interesting to know whether 
careful measurements would not reveal a physical dimorphism correlated with the 
physiological one. 
