BY WILLIAM A. HAS WELL. 



425 



A remarkable feature is that cilia are developed only on a 

 portion of the ventral surface, and are entirely absent round the 

 margin and on the dorsal surface. Along the anterior and 

 posterior margins open the ducts of numerous rhabdite-forming 

 glands the viscid secretion of which, with the contained rhabdites, 

 passes out from them, sometimes in considerable quantity. 



Locomotion is effected sometimes by the action of the cilia of 

 the ventral surface producing a slow gliding movement; at other 

 times the animal " loops " along actively, the adhesive anterior 

 and posterior regions being alternately fixed to and liberated 

 from the surface of the substratum after the fashion of suckers. 



The mouth has the appearance of a small transverse slit 

 situated on the ventral surface nearly on a level with the eyes. 

 The common genital aperture is a much smaller slit situated in 

 the middle of the ventral surface about a fourth of the total 

 length from the posterior margin. 



Alimentary System. 

 The pharnyx (ph.) is of the type termed by Von Graff 

 " pharynx doliiformis." Its length is about a sixth of that of 

 the entire body; its breadth somewhat less. In the substance of 

 its wall between the radial fibres are numerous large unicellular 

 glands, the ducts of which are arranged regularly and open into 

 the internal cavity close to the anterior margin of the pharynx. 

 The intestine (int.) has a thick wall composed of large vacuolated 

 cells full of granules which are collected into spherical masses, 

 some of which are of relatively large size. 



Nervous System. 

 The nervous system does not present any very noteworthy 

 features. The brain is a transverse band of fibrous material 

 situated on the dorsal side immediately in front of the anterior 

 margin of the pharynx, and of groups of nerve-cells connected 

 with this in front and at the sides. From the brain a single pair 

 of longitudinal nerve cords passes backwards close to the lateral 

 margins of the body. 



