KOFOID AND SWEZY: UNAEMOREU DINOFLAGELLATA 409 



Description. — The body has various shajjes, depending upon the degree of its inflation, age, 

 and food contents. It is especially liable to deformation and wrinkling, due to contraction and 

 local collapse of the periphery on capture and standing in the laboratory. The girdle rarely 

 affects the form materially, and even the sulcus fades out with the rounding up in old individuals 

 and as cytolysis approaches. The dinoflagellate structures, the girdle and sulcus, as well as the 

 effect of these upon the form of the body, are shown more clearly in the smaller individuals. 

 The smaller individuals have a proportionately deeper sulcus and a more reniform contour than 

 the larger ones, which tend to be more spheroidal, with only a slight flattening and shallow 

 excavation along the sulcus. Collapsed, or non-distended, small individuals may have the 

 anterior ends extended and somewhat pointed, or even flattened, by the rather rigid, barlike 

 extension of the precingular trough of the sulcus, and the posterior end may be extended by its 

 postcingular extension, terminating in the tentacle. 



In typical, distended, small (400//) individuals ("fig. KK, 1) the body is broadly subreniforra, 

 with the transverse diameter slightlj- exceeding both the dorsoventral and the longitudinal ones. 

 There is, however, much variation in proportions, due to contraction and collapse. The ventral 

 surface is deeply incised by the strictly longitudinal, median sulcus, which terminates posteriorly 

 in the tentacle and runs thence anteriorly in a straight line to its termination in the straight 

 apical trough, at or beyond the morphological apex of the epicone. The depth of the sulcus 

 varies in th.e several regions and is unlike in different individuals, according to the degree of 

 recession of the cj'tostome which lies in its deepest raidventral region. 



There are two main regions of the sulcus, the oral pouch containing the cytostome and the 

 apical trough. The oral pouch, when fully retracted (fig. KK, 2, o. p.), is a deep median pocket, 

 laterally compressed, at the bottom of which lies the central protoplasmic mass. The tentacle 

 is placed at its posterior end, the longitudinal flagellum traverses it lengthwise, the tooth lies 

 on its left face, and the proximal end of the girdle creases its left side. In lateral view the floor 

 of the oral pouch runs anterioiiy from the base of the tentacle to a level slighth' above that of 

 the equator, where it turns abruptly ventrad at right angles, forming the anterior lip (fig. KK, 1, 

 ant. I.) at a level with the general contour of the body. The cytostome lies in the bottom of the 

 oral pouch, as a linear region through which food is taken. Its exact limits are unknown. 



The apical trough (fig. KK, 1, op. tr.) is the continuation of the sulcus anteriorly towards 

 the apex. It emerges from the oral pouch over the anterior lip as a converging tract, and is 

 continued as a narrow, straight, shallow furrow to its abrupt termination near the apex. It is 

 supi)orted below the pellicle by an accumulation of protoplasmic processes and a tliickening of 

 the peripheral protoplasm. The trough may be slightly elevated above the general contour, and 

 appears to be a rather rigid structure. There is no evidence that it can function as a cj'to-stome, 

 as does some part of the sulcus within the oral pouch. 



The sulcus in other dinoflagellates with spiral girdle may be divided into precingular, inter- 

 eingular, and postcingular regions. These regions are recognizable in Nnctiluca. The pre- 

 cingular one includes the apical trough and that part of the sulcus within the oral pouch which 

 passes over the lip into the pouch and posteriorly to the proximal end of the girdle near the 

 tooth. A part of it within the oral pouch may function as a part of the cytostome. The inter- 

 cingular region is ill-defined owing to the absence of the distal end of the girdle. There is little 

 if any spiral deflection of the girdle in the zoospore and no evidence of such deflection in the 

 degenerate girdle of the adult. The distance between the proximal end of the girdle (fig. KK, 

 3, gii:) and the origin of the longitudinal flagellum which, in most dinoflagellates, represents 

 approximately the point of union of the distal end of the girdle with the sulcus may be held to 

 represent the intercingular part of the sulcus in NoctUuca. The postcingular part extends 

 from the origin of the longitudinal flagellum to the tentacle. 



The girdle (fig. KK, 3, git:), present in the zoospores (4) as a constriction below the sub- 

 hemispherical epicone. completely encircles the body. In the adult the girdle is degenerate, 



