128 LACINULARIA SOCIALIS 



In fact, the edge of the disc has a considerable thicivness, and 

 presents two ahvays distinct margins — an upper (/) and a lower {p')r 

 of which the former is the thicker, and extends beyond the latter. 



The large cilia are entirely confined to the upper margin, and,, 

 seated upon it, the}' form a continuous horseshoe-shaped band, which,, 

 upon 'the oral side, passes entirely above the mouth (fig. 4). The 

 lower margin (/') is smaller and less defined than the upper, its 

 cilia are fine and small, not more than i-4th the size of those of the 

 upper margin. On the oral side this lower band of cilia forms a 

 V-shaped loop (fig. 4), which constitutes the lower and lateral margins 

 of the oral aperture. About the middle of this margin, on each side,, 

 chere is a small prominence, from which a lateral ciliated arch runs 

 upwards into the buccal ca\-ity, and, below, becomes lost in the cilia 

 of the pharynx. 



The aperture of the mouth, therefore, lies between the upper and 

 lower ciliary bands. It is vertically elongated, and leads into a 

 buccal cavity with two lateral pouches, which give it an obcordate 

 form : these lateral pouches contain the lateral ciliated arches. A 

 narrow pharynx leads horizontally backwards from the lower part of 

 the buccal cavity, and becomes suddenly widened to enclose the 

 pharyngeal bulb in which the teeth are set. \\'here buccal cavity meets 

 the pharj'nx, a sharp line of demarcation exists (fig. 2). In Melicei-ta 

 two curved lines are seen in a corresponding position, and evidently 

 indicate two folds (PL II. [Plate 15] fig. 26), projecting upwards 

 into the oesophagus. In BracJiionus these folds are stronger (fig. 31), 

 while in Stephanoceros and Flosailaria this partition between the ceso- 

 phagus and what maybe called the crop is still more marked. From 

 the inner margin of the aperture in the partition two delicate 

 membranes hang down into the cavity of the crop, which have a wavy 

 motion, and it is to them, I think, that what Mr. Gosse describes as 

 an appearance of "water constantly' percolating into the alimentary 

 canal " is due. Dujardin had already noticed {I.e., p. 98) these 

 " vibrating membranes " in Flosailaria (' Infusoires,' p. 61 1). 



Between the pharyngeal bulb and the mouth there lies on each 

 side of the pharynx a clear, yellowish, horny-looking mass (/), which 

 sometimes appears merely cordate, at others, more or less completely 

 compcsed of two lobes. A similar structure exists in Brachionus and 

 Mclicerta. I believe its function is to gi\-e strength to the delicate 

 Avails of the pharynx, and that it is therefore to be considered as a 

 part of the horny skeleton.^ 



The general nature of the pharyngeal bulb and of its movements 



Leydig (loc. cil.) call.s these l^odies sacs, and considers them to be salivary glands. 



