THE WHEEL ANIMALCULES (ROTATORIA) 573 



(cf. p. 553). Of Stephanoceros there is but one species (Fig. 937), 

 while of Floscularia there are many, varying extremely in the form 

 of the corona. A few species have become free and swim about 

 in the open water (Fig. 935). The fact that they bear their tubes 

 with them shows that the free life has been secondarily acquired, 

 after the animals had become adapted to the attached condition. 

 All young Floscularias swim about for a time by means of moving 

 cilia. Just as do other rotifers. The males (Fig. 933, B) are free- 

 swimming throughout life. 



What relationship have the Flosculariidae to the typical rotifers 

 found in the Notommatidae? It must be remembered that not 

 all Flosculariidae have the extraordinary forms shown in Figs. 933 

 and 937. In some, the borders of the corona are not drawn out 

 into lobes, but. are smooth, as in other rotifers (see Fig. 936). In 

 others the cilia of the coronal edge are all, or partly, short and beat 

 regularly, like those of other rotifers; and about the mouth is the 

 same circlet of cilia found in other rotifers. Such Floscularias 

 approach much more nearly to the typical Notommatidae than do 

 the extreme developments along this line seen in Stephanoceros 

 and certain species of Floscularia. 



Furthermore, among close relatives of the notommatids are cer- 

 tain rotifers that seem to show transitional stages leading to the 

 Flosculariidae.^ In Microcodides and in Microcodon (Fig. 931), the 

 corona is formed on essentially the same plan as in the Floscularias, 

 and there are other peculiarities that seem to show that these are 

 transitional forms. In Microcodon, as in Floscularia, the corona 

 is the broadest part of the body; it has elevated edges, approaching 

 the net formation, and the mouth is in its center, with an inter- 

 rupted circlet of cilia about it. The foot in Microcodon as in Flos- 

 cularia forms a sort of long slender stalk, not ending in toes. But 

 in Microcodon it ends in a sharp point, while in Floscularia it ends 

 in a disk; this is doubtless because the former is still a free animal, 

 while the latter is attached. It is a most suggestive fact that Mi- 

 crocodon frequently places itself in the upright position, with the toe 

 attached by a thread of mucus, and thus remains for a time in a cer- 

 tain spot; such habits might readily lead to permanent attachment. 

 ' These important considerations are due to Wesenberg-Lund (1899). 



