376 PROCEEDINGS OF THE ACADEMY OF [May, 



base of the arms. Each of these cells then has a great extent, from 

 its base to the free tip of an arm. When the arms are fully extended 

 the outlines of the hypodermis seen on optical section appear even, 

 without any irregularities. But when the arms are partially retracted, 

 the hypodermis appears partitioned into circular areas on its inner 

 surface; on surface view these are seen as in fig. 13; and on optical 

 section as in fig. 12. At first I was inclined to consider these as 

 representing component small cells of the hypodermis, but the 

 absence of nuclei in them excludes that view and they can be regarded 

 only as folds of the continuous hypodermis due to the contraction 

 of the arm. The arrangement of the cilia upon the arms is very 

 complicated and has not yet been satisfactorily determined; it is 

 best seen on a living arm in a contracted condition. On the outer 

 as well as upon the inner surface of each arm the arrangement 

 of the cilia is shown by the dotted lines in fig. 12; there 

 the cilia are arranged in single rows, making angles together, these 

 single lines of ciha separated by spaces which are without cilia. But 

 on lateral view each arm shows a different arrangement of the cilia; 

 here (fig. 13) the cilia are arranged in tufts placed on oblique thickenings 

 of the surface of the hypodermis. In this figure only those cilia seen 

 in profile are drawn in extenso, while the insertion points of those on 

 the aspect of the arm toward the observer are represented by stippling, 

 each patch of fine dots denoting a tuft of cilia. At the tips of the arms 

 the ciha are more evenly arranged along the whole hypodermis. The 

 appearance of the tufts of cilia, arranged in oblique bands, are shown 

 for the two ventral arms under a lower scale of magnification in fig. 16. 

 The cilia are extensile, and in fully expanded condition attain a length 

 considerably greater than that of the arms themselves; but this is to 

 be seen generally only when the animal is under the pressure of a cover- 

 glass. I could not determine the presence of a cuticula upon the arms. 



The hypodermis of the foot is thickened, and at the junction of this 

 region with the trunk (figs. 9, 10) certain cells are very prominent. 

 These may correspond to the foot glands of the other Rotatoria, and 

 secrete the substance of the tube in which the animal lives. The short 

 peduncle (fig. 14) by which the foot is attached probably represents a 

 secretion of hypodei'mal cells at the distal end ; this peduncle is short, 

 hard and homogeneous. 



Alimentary tract. — By an oblique diaphragm {Dia., figs. 9, 10) the 

 cavity of the corona is divided into a more spacious infundibulum (Inf.) 

 and a more posterior vestibulum (Vest.), both of which have a nucleated 

 lining similar to that composing the hypodermis. The diaphragm is 



