170 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



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

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



FiG. 39.— DiagraniP showing the arrangement of the cilia of the trochal disk in the 

 Rotifira. I. Larval Lacimilaria. If. Adult Lacinularia. III. Philodina. IV. 

 Brachionus. V. Stephanoceron. J/, mouth ; G, ganj,'lion ; A, anus. 



Gated 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. 



Polyarthra and Triarthra possess long, symmetrically ar- 

 ranged, movably articulated setiB ; 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 Notoininata tardigracla^ however, the trochal 

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

 ture ; and there is no trochal disk in Apsiliis, Lmdia, Ta- 

 phrocaynpa, and Balatro. Some few Rotifera are parasitic. 

 Thus Albertia is an entoparasite, and Palatro an ectopara- 

 site, upon oligochastous Annelids. 



Under the name of Gasterotricha^ Metschnikoff and Cla- 

 parede * include the curious aquatic genera Chmtonotus, Ich- 

 thydium^ Choetura, Cephalidium^ Dasyditis, TurhaneUa^ and 

 Hemidasys^ the last of which alone is marine. These animals 

 have been united with the Botlfe^'a, but thej' 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 



* Claparede and Metschnikoff, "Beitrtige zur Kenntniss der Entwickelungs* 

 gescbichte der Chactopoden," 1868. 



