170 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



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

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



Fig. 39.— Diagrams showins; the arrani^ement of the cilia of the trochal di?k in the 

 Rotiftra. I. Larval Lacinularia. II. Adult Lacinuluria. III. Philodina. IV. 

 Bruchionus. V. Stephanoceros. J/, mouth ; G^ ganj^liou ; A, anus. 



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

 is a median process of that face cf 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. 



Polyarthra and Triartlira possess long, symmetrically ar- 

 ranged, movably articulated set» ; and Pedation has median 

 appendages proceeding from both the neural and the opjoosite 

 faces of the bod}^, 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 Nototiimata tardigrada^ however, the trochal 

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

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

 phrocampa^ and Palatro. Some few Rotifera are parasitic. 

 Thus Albertia is an entoparasite, and Palatro an ectopara- 

 site, upon oligoch^tous Annelids. 



Under the name of Gasterotriclia^ Metschnikoff and Cla- 

 parede ^ include the curious aquatic genera Choitonotus^ Ich- 

 thydium^ Chmtura^ Cephcdidium^ Pasyditis, TurhaneUa^ and 

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

 have been united with the Rotifera^ but they differ from them ' 

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

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



^ Claparede and Metschnikoff, "Beitrilge zur Kenntniss der Entwickelungs* 

 geschichte der Chaetopoden," 1868. 



