THE WHEEL ANIMALCULES (ROTATORIA) 569 



7. Dinocharidae. Scandium (Fig. 903) is perhaps essentially a 

 Furcularia which has developed a long foot and long toes, for leap- 

 ing (compare Furcularia longiseta, Fig. 871). Dinocharis (Fig. 904) 

 and Polychaetus (Fig. 905) are perhaps further developments, some- 

 what divergent, along the same line. All these animals are given to 

 springing about wildly by the aid of powerful strokes of the foot 

 and toes; the same habit is found in various species of Furcularia. 



Next may be taken up a Hne of divergence from the central 

 Notommatidae that leads to some extraordinary forms. It pro- 

 duces the great families of the Hydatinidae, the Notopsidae, the 

 Ploesomidae, and the Brachionidae, with their relatives. Here de- 

 velopment has proceeded both toward greater strength and activity 

 and toward protective armor, so that the result is to produce some 

 of the most powerful and ferocious rotifers that exist. 



8. Hydatinidae. The close connection with the Notommatidae 

 is seen in the Hydatinidae. The well-known rotifer Hydatina senta 

 (Fig. 906) was formerly classed with the Notommatidae. It has a 

 soft, segmented body, small foot and toes, ventral corona, — aU as 

 in the primitive genus Proales. But the corona (Fig. 906, B) is 

 large and differentiated in a way that is characteristic for the 

 families making up the present group. Around the outer edge of 

 the corona the cilia form a prominent wreath, while about the 

 mouth is another series of cilia so interrupted as to form three 

 groups, one dorsal and two lateral (Fig. 906, B). In the region 

 between the outer and inner series of ciHa are certain prominences 

 (three in Hydatina), on which the cilia have become long, stiff 

 setae, doubtless serving as sense organs. The coronal area between 

 the parts thus far mentioned retains in Hydatina senta a portion of 

 the covering of fine ciha primitively found in Proales; in most other 

 members of this group these fine ciha have quite disappeared. 

 The jaws are of the peculiar type shown in Figure 906, C. 



9. Notopsidae. The next step in differentiation is seen in Notops 

 (or Hydatina) hrachionus (Fig. 909) . The cuticula, while still soft, 

 has become a Httle stiffened, so that the body tends to hold its 

 form; the foot is more prominent. 



The next steps seem to be as follows: Notops clavulatus (Fig. 912) 

 and Triphylus lacustris (Fig. 908) are rotifers showing still the soft 



