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substratum ; many of them are really mainly sedentary animals. The more the Ro- 

 tifers pass over to a swimming motion, the more the foot loses its importance as 

 a creeping organ; it is now mainly used partly as a steering organ partlj' as an 

 organ of attachment. In accordance with the first named function, but in very dif- 

 ferent waj's, it is now almost always conspicuously separated from the other part 

 of the bod}^; only in the Synchœladœ where parts of the wheel-organ (the auricles) 

 play the rôle of steering organs, the foot is the typical foot of the creeping Rotifers 

 now only used as an organ of attachment. 



In the freeswimming Rotifers the foot has a very different shape but is often 

 formed in accordance with its main function of steering organ. This for instance 

 is the case with the foot in the two families Salpinadœ and Euchlanidce where it 

 may be shown how the broad toes are used; this is also the case with the annulated 

 foot of Pterodina, Ploesoma, further with many of the Brachionidcc, where the foot 

 is only used at the special moment when the direction of the movement is to be 

 greatly altered; during the slowly rotating motion, the foot is often withdrawn into 

 the lorica, especially in one of the most pelagic species B. pala. Still it preserves its 

 significance as an organ of attachment. In many of the plancton Rotifers the foot 

 glands either atrophiate or are feebly developed. 



Very many of the true plancton Rotifers have no foot at all ; they are therefore 

 unable to attach themselves {Asplanclina, Triarthra, Pohjarthra, Pompholyx, Pedalion, 

 Anurœa, Notholca, Ascomorpha, Anapiis) and if not provided with leaping thorns 

 unable suddenly to alter the direction. 



Even if the foot disappears, it is not quite certain on that account that the 

 foot glands also disappear. Many of the plancton Rotifers carrj' their eggs glued to 

 the posterior part of the body, in Pomphohjx fastened by a peculiar system of threads, 

 which can be pushed out and in from an apical opening. Further investigations will 

 show if the glutinating matter is derived from rudimentary foot glands which have 

 undergone a change in function. 



Among the slowly swimming inhabitants of the small ponds, covered with 

 carpets of leaves, and those from the pelagic region of the lakes, with regard to the 

 reduction of the foot there exists the most beautiful series of reductions (e. g. Hydatina, 

 Notops brachionus, Brachionus, Anurœa. — further Asp/anc/inopus, Asplanchna Herricki: 

 Asplanchna priodonta. — Species of the genus Synchœta and of the Ploesomatidœ show 

 other examples in the same direction. — Peculiar foot forms are especially found 

 among the half swimming, half creeping, Rotifers of the ponds e. g. the jumping 

 foot of Scaridium, Dinochavis and some Furciilaria-species. Even if the foot among 

 freeswimming Rotifers is used as a steering organ still it is in very many cases 

 here also used as an organ of attachment; ver}' many of the so-called freeswimming 

 Rotifers are in a still higher degree than commonly supposed fixed animals, which 

 the net has thrown off from their substratum and which live a more swimming 

 life in the vessels than in nature. Even among the freeswimming Rotifers we often 

 find very peculiar structures of the foot glands; these organs may develop to a very 



