nowlin: a new holotrich. 293 



on the right ventral area of the animal, and because the animal 

 moves often on the edge we are apt to think of this ciliated 

 region as purely ventral. Lankeste in describing the family 

 Dysterina, to which I believe this specimen belongs, calls this 

 the ventral side. The right ventral groove then extends from 

 the posterior end of the animal completely along the side and 

 rounds across the cephalic end. At its caudal extremity is an 

 appendage, and at the cephalic, a long flagellum. 



EXPLANATION OF TEXT FIGURES. 



The figure to the left is a view of the right dorsal side of the animal, 

 showing the flagellum anteriorly and the ventral cilia; the calcareous 

 supporting rods of the mouth, the two contractile vacuoles and tho 

 nucleus. The caudal appendage is shown by a continuous line and its 

 range of motion by dotted lines. 



The middle figure is a view of the animal on edge, showing a convex 

 dorsal side, concave ventral, left dorsal groove and caudal appendage. 



The right figure is an imaginary cross-section through the nucleus. 



The tail, like the body, is covered by the silicious skeleton 

 and appears hollow, at least part of the way. Whether the 

 anus lies at its distal end, as is claimed for Onychodactylus, I 

 am unable to say. Its range of movement is nearly 180 degrees 

 in the plane of the right ventral groove. In movement the ani- 

 mal may use this organ as a propeller, shoving itself forward 

 with long strides by placing the end against a solid structure. 

 It is this motion which resembles strongly that of a rotifer. In 

 swimming the tail is usually folded into the groove like a knife- 

 blade closed in its handle, and the animal is carried forward 

 by the vibration of its cilia. The animal when creeping over a 

 solid surface stands on the ciliated edge, much as a mussel when 

 moving through the sand. In swimming it lies slightly on its 

 ventral side and has a swinging motion through the water. 



The flagellum is located in a deep depression of the cephalic 

 protoplasm. On superficial examination this depression might 



