168 



Transactions of the Society. 



the naked eye. It was observed in eight instances, in each alone, 

 and always inclosed in a group of Megalotrocha, above which, from 

 its greater size, it towered like a giant in a crowd. . . . Acijclus is 

 translucent whitish, with the thicker part of the body yellowish or 

 brownish, due to the colour of the capacious intestine shining 

 through the integument. It was difficult to obtain a clear and 

 accurate view of the exact mode of attachment and the internal 



structure of the animal, from its 



Fig. 31. 



Fig. 32. 



Head. 



incessant motions, its becoming 

 wrinkled in contraction, and 

 from its being obscured by the 

 surrounding bunch of Megalo- 

 trocha. . . . The head is in the 

 form of a cup prolonged at the 

 mouth into an incurved beak. 

 It is retractile, protrusile, con- 

 tractile, and expansile. When pro- 

 truded and expanded the mouth gapes 

 widely, and the beak becomes more ex- 

 tended, but always remains incurved. 

 The mouth is bordered by a delicate 

 membrane extending to the rounded end 

 of the beak, and presenting a festooned 

 appearance. ... In contraction of the 

 head or oral cup it is reduced to half 

 the bulk of its expanded condition, while 

 the mouth is constricted and the beak is 

 rolled in a single spiral inwardly, as seen 

 in fig. 32. The extension of the head 

 below forms a narrowed and transversely 

 wrinkled neck, which expands into the 

 body. The expansion and contraction 

 of the head appear to be due to the flow 

 of a milky liquid between the coelum or 

 body-cavity and intervals in the walls of the oral cup or head. 

 The retraction of the latter is produced by longitudinal muscles, 

 which may be seen in the Tvall of the cup extending from the 

 wall of the body just below the neck to the festooned membrane 

 bordering the mouth . . . The oral cavity converges in a funnel- 

 like manner to a pouch occupying the neck. The pouch is seen to 

 contract and expand from time to time, but it was indistinctly 

 defined. At the bottom of the pouch there is a small mastax, or 

 muscular pharynx, provided with minute jaws." Professor Leidy 

 goes on to say that the jaws have a parallel series of about twenty 

 teeth, that the tail is occupied with retractor muscles extending 

 from the walls of the body, that the interval between the stomach 



Acyclus inquietus. 

 Entire animal. 



