170 THE ANATOMY OF INVERTEBRATED ANIMALS. 



and sometimes telescopically-jointed " foot," usually termi- 

 nated by two styles, which can be approximated or divari- 



Fig. 39.— Diagrams showing the arrangement of the cilia of the trochal disk in the 

 Botifera. I. Larval Lacinularia. II. Adult Lacinularia. III. Philodina. IV. 

 Brachionus. V. Stephanoceros. M, mouth ; G, ganglion ; A, anus. 



cated like pincers, and serve to anchor the body. This foot 

 is a median process of that face of the body which is opposite 

 to that on which the ganglion is placed, so that it is not the 

 homologue of the peduncle of the tubicolous forms. 



JPolyarthra and Triarthra possess long, symmetrically ar- 

 ranged, movably articulated setae ; and Pedalion has median 

 appendages proceeding from both the neural and the opposite 

 faces of the body, as well as lateral appendages. 



In most of the free Rotifers the trochal disk is large ; it 

 may be bilobed or folded upon itself (Fig. 39, III.), or its sur- 

 face may give rise to ciliated processes (Fig. 39, IV.). In 

 Albertia and Notommata tardigrada, however, the trochal 

 disk is reduced to a small ciliated lip around the oral aper- 

 ture ; and there is no trochal disk in Apsilus, Lindia^ Ta- 

 phrocampa, and JBalatro. Some few Rotifera are parasitic. 

 Thus Albertia is an entoparasite, and JBcdatro an ectopara- 

 site, upon oligochsetous Annelids. 



Under the name of Gasterotricha, Metschnikoff and Cla- 

 parede 1 include the curious aquatic genera Chcetonotus, Ich- 

 thydium, C/icetura, Cephalidium, Dasyditis, Turbanella, and 

 Ilemidasys, the last of which alone is marine. These animals 

 have been united with the JRotifera, but they differ from them 

 in the absence of a mastax and in the disposition of the cilia, 

 which are restricted to the ventral surface of the body. It 



1 Olaparede and Metschnikoff, "Beitriige zur Kenntniss der Entwickelungs- 

 geschichte der Chaetopoden," 18G8. 



