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EY C. T. HUDSON, M.A., LLD. 



Abstract of a Lecture on Nov. bth, 1874. 



IT is now half a century or more since Ehrenberg published 

 his great work on the Rotifera, and the classification which he 

 then adopted still holds its ground — not because it is satisfactory, 

 but because no one has as yet been able to supplant it by a better. 

 Ehrenberg divided the Eotifers into three great groups, according 

 to the forms of their trochal discs, and each group into a sub- 

 division, according as the animals contained in it were loricated, 

 or illoricated, and each sub-division into families — one of the chief 

 characteristics of which was the presence or absence of red eye- 

 spots. 



Unfortunately, every character upon which Ehrenberg relied 

 for the above classification has failed to stand the tests applied 

 by modern research and bettor instruments. The trochal discs 

 (though still not entirely understood) are seen to be very difi^erent 

 from the simple forms figured by the Professor ; the red spots are 

 by no means always eyes — where they are eyes they sometimes 

 disappear in the adult animals, and when they are not eyes, they 

 are very variable in number and position : in fact, neither trochal 

 discs nor red spots jdeld good characters for classification. As to 



