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two wreaths, and conveyed further to the mouth. In this case the mouth parts have 

 no significance or only a slight significance for catching the food, and do not reach 

 the mouth opening; in some families they are far removed from it. It reaches its 

 highest development in Pedalion among the plancton Rotifers and in the Melicertidœ 

 among the sessile Rotifers. In some of the plancton Rotifers such as Triarthra, Poin- 

 pholyx; Pterodina, it is only faintly developed. Below the ciliary wreath there is here 

 a faintly developed furrow, covered with very fine cilia, but this space is not lim- 

 ited here by a lower ciliary wreath. To this type also belongs the wheel-organ of 

 the Philodinidce built in another way, but also destined to be used simultaneously 

 for locomotion and for gathering nourishment. In many of the almost sessile raoss- 

 Philodinidœ it is used almost exclusivelj' in this way; here its significance as a lo- 

 comotory organ is almost lost. This is also the case with the wheel-organ in some 

 of the above-named types, some of them being almost sessile organisms; this f. i. is 

 the case with many of the Brachionidœ which, once fastened to a substratum, only 

 very rarely leave it. (B. råbens upon Daphnids). By means of a peculiar structure it 

 obtains significance also as a tube forming organ in some of the Melicertidœ. A very 

 peculiar wheel-organ occurs in the Flosculariidœ which can only be understood on 

 the view that we have here organisms which are simultaneously sessile and ani- 

 mals of prey (de Beauchamp). The disc is here formed like a funnel whose borders 

 commonly taper into lobes and arms which carry long stiff cilia. Centrally at the 

 bottom of the funnel lies a second chamber, the vestibulum, encircled by a horse 

 shoe-shaped ciliated rim, and in the base of the vestibulum is a long slit, the buccal 

 orifice, bounded by two chitinous lips. Organisms which have got into the funnel, 

 cannot get out because of the long bristles which extend over its orifice; when 

 victims enough are gathered in the vestibule they are swallowed down into the ali- 

 mentary canal. 



Wheel-organ, males. If we will now try to understand the wheel-organ of 

 the males we must remember that apart from a few rather doubtful exceptions, 

 it is only an organ of locomotion and has nothing to do with procuring food. 

 The alimentary canal is obliterated or rudimentarj' and the animal gets no food 

 whatever. 



It must further be remembered that, whereas the females of the Rotifera, when 

 swimming, mainly move along a screw line, the males mainly move along a straight 

 line. As far as I understand, when the animals are moving along a screw line it is 

 most probablj' impossible to steer towards a definite point, especiallj' when this 

 point is moving. They are unable lo follow a moving prey or a rotating female. We 

 therefore see that the few plancton-Rotifers which in the female sex live on other planc- 

 tonts which are seized and sucked out, i.i.Ploesoma Hudsoni, in the male sex really often 

 follow straight lines, at all events when they are in pursuit of prey. With regard to the 

 males of the Rotifers which are always in search of the females during their short life 

 time it would be almost impossible for them to find and reach a female when discovered, 

 if the motion were only rotating. It is in accordance with this that the males almost 



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