572 FRESH-WATER BIOLOGY 



The typical Asplanchnas are beasts of prey, the jaws forming a 

 great pair of forceps which can be thrust from the mouth to seize 

 other large animals. Asplanchna herrickii de Guerne and A. pri- 

 odonta Gosse (Fig. 929) are important elements of the plankton of 

 lakes. In the Great Lakes they sometimes swarm so densely that 

 a net dipped into the water captures thousands. Other species of 

 the Asplanchnidae live among water plants. 



16-18. Floscularida. Now come certain groups of rotifers that 

 seem at first view to differ markedly in almost every respect from 

 the notommatids. The Flosculariidae (Figs. 933 to 936) live attached 

 in tubes. The foot has become a stalk for attachment; there are 

 no toes. The corona is immensely large, forming a great lobed 

 net of thin membrane, which can be spread widely and serves to 

 capture living prey; the mouth lies in the center at the bottom of 

 this net. The cilia about the edge of the corona have become enor- 

 mously long and slender rods or threads, which do not beat as cilia 

 usually do, but may be moved about so as to aid in entangling prey. 

 In connection with the method of feeding on large animals thus cap- 

 tured, the alimentary canal (Fig. 934) has become greatly devel- 

 oped. The upper part of the coronal net forms a great funnel, called 

 the infundibulum (i), partly closed off below by a ring-like fold, 

 the diaphragm (d), which has about its edge an interrupted cir- 

 clet of cilia. The opening through the diaphragm leads into a 

 second chamber, the vestibulum (v), at the bottom of which is the 

 mouth (m). From the mouth there hangs the slender esophageal 

 tube (0) ending freely below. The food after passing through this 

 reaches a third large cavity, the proven triculus (pr) . It is only at 

 the posterior part of this that the mastax (mx) and jaws are reached ; 

 so that all thus far seen corresponds merely to the short mouth 

 cavity lying in front of the jaws in other rotifers. The trophi 

 (Figs. 934 and 933, D) are peculiarly modified, the unci forming a 

 pair of two-tined forks which are the main part of the jaws, though 

 the other typical parts can be distinguished. 



The Flosculariidae include two genera, Floscularia (Figs. 933 to 

 936) and Stephanoceros (Fig. 937). The numerous species are found 

 abundantly seated in transparent tubes attached to plants; they 

 are among the most attractive objects known to microscopists 



