574 FRESH-WATER BIOLOGY 



All together, Microcodon seems to form a link between the Flos- 

 culariidae and the Notommatidae. Microcodon itself is closely 

 connected with the Notommatidae by the transitional species be- 

 longing to the genus Microcodides (Fig. 932). These have corona, 

 body, and toes more nearly on the notommatoid plan. The two 

 genera make up the family Microcodonidae. 



Specialization going even beyond that in the Flosculariidae is 

 seen in Apsilus (Fig. 938) and Atrochus (Fig. 939). In these ex- 

 traordinary rotifers the ciHa have been completely lost. The 

 compHcated structure of the alimentary canal shows their close 

 relationship to the Flosculariidae. In the young the ciHa still 

 exist, and the animals swim about by their aid. 



19-22. Melicertida. Another group of extraordinary and at- 

 tractive rotifers is that of which Melicerta (Fig. 948) is the repre- 

 sentative. These were formerly classified with the Flosculariidae, 

 the two forming the group Rhizota. But it is evident that the 

 two families differ widely, and that the group Rhizota is not a 

 natural one. The Melicertidae are found, like the floscules, at- 

 tached to aquatic plants, often in great numbers. Many Hve in 

 tubes, and the species of Melicerta manufacture their tubes in a 

 most interesting manner, as is well described in Hudson and Gosse 

 (1889). 



The most important peculiarity of the Melicertidae is perhaps 

 the corona. This is a large disk, bare within, but having around 

 its outer edge a series of strong ciUa, just as in many other rotifers. 

 But in this group is found a special peculiarity. This outer wreath 

 is differentiated into two series of cilia, running parallel around the 

 disk (Fig. 865). The inner series has much larger cilia than the 

 outer one, and between the two is found, in most cases, a groove. 

 This groove is often lined with fine cilia. Along the groove small 

 food particles are carried to the mouth, situated on the ventral 

 side. In some genera the disk is drawn out to fonn two, four, 

 or eight lobes, giving the animal an extraordinary appearance 

 (Fig. 950); in other cases it is nearly circular (Figs. 865, 951, 952). 

 Throughout this group the jaws are of a pecuhar type (Fig. 866), 

 known as the malleo-ramate. As a rule the animals have two eyes. 



The more extreme types of this group seem to stand far from 



