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The Swimming Peculiarities of Daphnia and its Allies^ 

 with an account of a new method of examining living 

 Entomostraca and similar organisms. 



By D. J. Scourfield, F.R.M.S. 



{Read Octoher Idth, 1900.) 



The genus Daphiia, as understood by Baird and other of the 

 older writers on Entomostraca, has for some considerable time 

 been recognised as embracing four types of animals to which the 

 names Daphnia, Ceriodaphnia, Simocephalus, and Scapholeheris 

 have been given. The separation of the old genus into these 

 four new genera, although at first, perhaps, hardly based on 

 sufficient evidence, has been abundantly justified, for the more- 

 we study these animals the greater becomes the number of the- 

 features characteristic of each type. But I do not wish to enter 

 now into all the differences existing between Daphnia and its 

 closest allies. I simply wish to point out that in addition to 

 the morphological distinctions there is also a fundamental 

 difference in the swimming habits of Daphnia and C eriodajyhnim 

 on the one hand and ^imocephalus and Scapholeheris on the 

 other, for whereas the two former always swim either vertically,. 

 or obliquely back uppermost, the two latter always swim more 

 or less obliquely back downwards. These peculiarities in the 

 method of progression in the water are so constant that, if the- 

 animals are seen swimming, it is absolutely impossible to mistake 

 say a Daphnia for a Simocephalus, even with the naked eye. 



From the moment when I first recognised this important 

 distinction between the two pairs of genera mentioned, I havfr 



