of the Bay of Naples. 93 



at rest ; at each movement of the maxilltB it is, on the con- 

 trary, more or less elongated transversely. It leads into a 

 short, canaliform, buccal cavity, into the bottom of which 

 project the denticles of the mastax, wliich, dorsally, enclose 

 between them the orifice of the oesojjhagus (fig. 6). At the 

 first glance it seems as if the masticatory apparatus in Seison 

 and Paraseiso7i lay in a special appendage of the oesophagus, 

 and thus differed from the condition in the freshwater Rota- 

 toria ; but as, in the latter, the oesophagus likewise always 

 opens dorsally into the masticatory apparatus, although 

 usually towards the middle or the hinder end of it, there is, 

 in these genera, only a considerable displacement forwards of 

 the oesophageal aperture. 



The masticatory apparatus forms two divisions — the teeth, 

 which project forward into the buccal cavity, of which two 

 pairs are present (fig. 9, I. and il.), and a supporting appa- 

 ratus, bearing these, and placed further back (figs. 8, 9, a, /3, 

 y). The latter consists of three pairs of rather large chlti- 

 nous ossicles, of which the middle one (a) far exceeds the 

 others in length, and therefore at once catches the eye. It 

 forms two thin spatuliform laminse, much narrowed in their 

 anterior half, where they unite to form a single pointed rod, 

 as is best seen by examination from below (fig. 9). At the 

 posterior extremity the two laminai certainly lie very close 

 together, but by a fine median line they show the original 

 double nature of the whole structure. The broad surfaces of 

 the laminge bear about nine longitudinal costse, which are 

 strongly marked posteriorly, but terminate in front in ex- 

 tremely delicate lines. To the right and left of this median 

 piece (a) of the supporting apparatus lie two ossicles, one of 

 which (/3) bends somewhat outwards and downwards, and the 

 other (7) in a large curve upwards ; this latter dorsal member 

 does not extend quite so far backwards as the ventral one, of 

 which it must further be mentioned that its posterior extre- 

 mity is widened like the bowl of a spoon, while the anterior 

 end curves slightly outwards and is directly applied to one 

 of the teeth. At the point where the chitinous pieces 7 and ^ 

 meet there is also a small rib directed backwards (fig. 9, h). 

 The two pairs of teeth, which are firmly united with the 

 above-described supporting pieces and are moved by them, 

 are of different forms. Two teeth form little rods, which foik 

 into two short points at the anterior end (fig. 9, i.). They are 

 supported by the pieces indicated by y. The two other teeth 

 are stout, elongate, ovate structures, which abruptly become 

 narrower in front. The reciprocal movement of these teeth 

 is effected by stout muscles, which spring from the costse of 



