121 309 



sex (Dinocharis, Scaridium), it is reduced to a simple swimming organ in tlie male 

 sex. As the males of the fixed Rotifers, the Melicertidœ and Flosculariidcv are always 

 freeswimming organisms, never living in tubes, the foot of these species is not 

 provided with all those peculiarities which characterise the female foot in these 

 families, and which help the females to sink down in the protecting tube. All in all 

 it will be understood that the foot in the male sex is a much more reduced organ 

 than in the female sex. As a swimming organ it has lost its significance in many 

 families; but it has preserved its significance as an organ of fixation. In accordance 

 herewith the foot glands onlj' rarely disappear. The substratum upon which the 

 males mainly use the foot is the body of the female; therefore it has mainly signi- 

 ficance during the mating process. It disappears for the benefit of the development 

 of the penis which is partly formed b}' means of blood pressure upon the dorsal 

 side of the foot. 



Wheel-organ. Female. As mentioned above the wheel-organ of the lioti- 

 fera was formerly interpreted as consisting of two zones of cilia, the inner one 

 termed trochus the outer termed cingulum, both encircling a circular funnel and 

 with a fineh' ciliated groove between them. This is the interpretation of Leydig, 

 Huxley and Plate. This view was adopted as late as 1910 (Hartrog). As mentioned 

 above already Metchnikov and Joliet, later on myself and lastly de Beauchamp 

 have tried to show that the original wheel-organ of the Rotifera is really a ventrally 

 situated ciliated disc ("la plaque ciliée buccale" de Beauchamp). In the most prim- 

 itive types (some of the Notommatidœ and the Adinetadœ) this ciliated disc without 

 any bordering zone of longer cilia is still preserved. This ciliated plate is simul- 

 taneoush' an organ of locomotion with which the animal moves slowly over the 

 substratum, partly an organ with which the food is brushed off into the mouth; 

 the organ cannot be used for swimming, and the animals creep in Turbellaria-manner 

 over the substratum. As the Rotifera accustomed themselves to the swimming mo- 

 tion, the cilia at the borders of the disc were forced to overcome a much greater 

 resistance than those covering the centre of the disc. The result was the development 

 of the bordering zone of cilia, the "bande circumapicale" de Beuchamp. In the most 

 primitive types this band is in the main only developed in quite particular lateral 

 parts of the disc, and these parts, the socalled auricles (oreillettes) or "Wimperohren", 

 are then capable of being withdrawn and extended again. When withdrawn, the 

 animal is still a creeping, when protuded, a swimming animal (many Notommatidœ). 

 They are especially well developed in those families where the foot is not well 

 marked off from the other part of the bod}', and preserved in those swimming 

 families where the foot cannot therefore be used as a steering apparatus, the auricles 

 being used in this way (some Notommatidœ, Syncluvtadu'). 



Simultaneously with the development of a wheel-organ, consisting of a ciliarj' 

 disc, bordered by a more or less continuous row of longer cilia, the position of the 

 disc is altered from a more ventral to a more vertical one. The more the animals 



D K. D. Vidensk. Sclsk. Skr., naturv. og mathcm. Afd.. 8. Riekke. IV. 3. ^j 



