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Brachionus bakeri and its Varieties. 



By Charles F. Rousselet, F.R.M.S. 



Plate XVI. 



{Read January 15th, 1897.) 



It is now a well-known fact that many species of Rotifers 

 are liable to considerable variation, and none more so than the 

 different members of the genus Brachionus. This variation has 

 given rise to a great amount of species making, not less than 

 eight specific names having lately been given to varieties of a 

 single form. 



The object of this paper is to show to what extent variation 

 occurs in Brachionus bakeri, and so to prevent, if possible, the 

 making of new species and avoid the confusion arising there- 

 from. 



Brachionus bakeri was named by 0. F. Miiller (1786) in honour 

 of Henry Baker, the English microscopist, who flourished about 

 the middle of last century, and who, in 1764, published a work, 

 " Employment for the Microscope," in which, amongst many 

 other curious things, he described and figured several Rotifers. 

 In Fig. 11 I give an exact copy of Baker's illustration of the 

 animal which now bears his name. He says in the text that he 

 found it first in 1745, " together with two other sorts of wheel 

 animals having shells, inthe water of the cistern in the garden 

 of Somerset House." Ehrenberg's figures of B. bakeri are very 

 good, and like my Fig. 10, with slightly larger anterior and pos- 

 terior spines. In his description Ehrenberg mentions some 

 characteristic features which unfortunately have not been re- 

 peated by Mr. Gosse, whose diagnosis of this species in The 

 Rotifera is singularly incomplete, and in part inaccurate. Mr. 

 Gosse mentions two small spines bounding the orifice of the 

 foot, which are not spines at all in any sense. 



The two most characteristic features of B, bakeri, common to 



