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walers; what occurs of these great divisions in freshwater, is only to be regarded 

 as remnants, separated from the main stock, often in the dawn of the earth. As far 

 as I have been able to see, the Rotifera is the onlv di\"ision of freshwater organisms 

 which cannot be regarded from this point of view. It seems as if their developmental 

 centre has really been in the freshwaters: they are almost lacking in the sea, and 

 apart from the very aberrant Seisonacea, they never develop special forms there. 

 That the land Rotifera, the moss fauna of the frees, derive from freshwater, needs 

 no farther explanation. Owing to this view, which is allowable, especially with regard 

 to animals about whose Phylogeni Palæontology gives no answers at all, 1 am dis- 

 inclined to see near relationship with marine animals. 



The ^ew given above is further sfrengthened by the following fact. If we look 

 over the other freshwater organisms with marine derivation, it is easy to show that 

 the members of these different divisions, the Spongia, the Brgozoa, the Coelenterata, 

 the Crnstaœa, the Fishes, are a remarkably casual medley of organisms, the affini- 

 ties of which are often either much nearer to marine organisms than to freshwater 

 organisms belonging to the same division of animals, and with which thev live side 

 by side. At the present time they very often show no affinities at all with organisms 

 from this very geological epoch, whereas their affinities with extinct marine animals 

 are regarded as estabUshed facts. However different the Rotifera may be. this view 

 cannot be shared with regard to them; just this verj- peculiar phenomenon, that 

 so very many of the families of the Rotifera may be arranged in developmental lines 

 ■with their exfreme stages finishing in plancton organisms, and with their starting 

 points traced back to creeping organisms, gives support to the idea that they have 

 a common source. 



That further all these developmental lines really originated in freshwater and 

 not in the sea, is in my opinion obvious, because during their development they 

 adapted themselves biologically in accordance "«ith those rules which many other 

 freshwater organisms have been forced to follow, if exactly this element, the freshwater 

 of the earth, was to be used as a home for these organisms. I am here thinking 

 especially of the propagation, the heterogoni, the great rôle the resting eggs play in the 

 life of the Rotifera, the absence of larva stages, all phenomena which the Rotifera share 

 with so many other freshwater organisms, and which can only be pointed out in a very 

 sUght degree or not at all in the marine fauna. That the reduction of the male sex 

 may be partly observed from the same point of view, 1 shall tn," to show later on. 



If the above-named supposition, that the freshwater is the native home of the 

 Rotifera is correct, and if further it is correct that the creeping, slowly swimming 

 bottom and httoral forms are the most primitive forms, the Tarbellaria must be 

 regarded as those freshwater organisms from which we are best able to frace the 

 derivation of the Rotifera. Simultaneously it wiU be understood that I am only with 

 difficulty able to share the views of de Beauchamp, according to which the Rotifera 

 should be more or less related to a great number of marine animals. My view is 

 especially based upon the sfrueture of the excretory organs, common to both divi- 



