410 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



and, though figured by Webb (1855, pi. 6, fig. 6) and Robin (1878, pi. 36, fig. 4; pi. 41, fig. 24), 

 it otherwise e.scaped their attention, as it has that of all other investigators of Noctiluca. We 

 have found this structure repeatedly in living Noctiluca and regard it as the proximal end of 

 the girdle and not a mere wrinkle due to contraction. Its constancy in position, when present, 

 its well marked borders and the supporting peripheral ej'toplasm confirm this interpretation. 

 Its location and morphological relations are precisely those of the proximal end of the degenerate 

 girdle. It is a shallow, arched trough, arising on the left side of the sulcus just anterior to the 

 base of the longitudinal flagellum and adjacent to the tooth. It makes from 0.08 to 0.20 turn 

 about the body, dying out distally. It lies near the level of the equator and marks the line of 

 incomplete separation of epicone and hypocone which, in Noctiluca, would thus be subequal. 



The transverse and longitudinal flagella are represented respectively by the tooth and the 

 small longitudinal flagellum. The former (fig. KK, 3, tent.) is a small mobile projection which 

 lies at the left and slightly anterior to the base of the longitudinal flagellum, adjacent to the 

 proximal end of the girdle in the edge of the sulcus. It is a somewhat rigid, striate membrane, 

 overarching the sulcus to its right. Its form varies in published figures and in individuals 

 which we have observed. In its most reduced form it is a small, low, ragged ridge. It may 

 form only a single arched tooth, or a bifid one, or a series of two or three teeth, increasing in 

 length anteriorly, or it may rarely appear as a rather ragged tapering or broad and ribbon-like 

 process half as long as the longitudinal flagellum projecting free into the sidcxis. In life it is 

 subject to spasmodic downward strokes into the adjacent sulcus and to minute changes in out- 

 line. It is not, as we have seen it, freely undulating as is the transverse flagellum typically, but 

 rather rigid and slow in movement. It appears to be a transverse flagellum adapted as a 

 prehensile organ for the capture and ingestion of organisms taken as food. For this function 

 it has become more rigid and has lost its distal extension, locomotor function, much of its 

 mobility, and its location in the girdle. It lies in the sulcus immediately adjacent to the proximal 

 end of the degenerate girdle and runs longitudinally instead of transversely. However, it is 

 longest near the end of the girdle. No trace of it is shown in the zoospores by Cienkowskv- (1871), 

 Robin (1878), or Ishikawa (1899^, provided that the tentacle-like structure shown by Cien- 

 kowsky and Ishikawa becomes the tentacle of the adult, as seems probable. No account of the 

 transformation of the zoospores into the adult is available. 



The longitudinal flagelliim (fig. KK, 3, long, fl.) is of the usual form, a simple thread. It is, 

 however, much reduced in length and lies hidden in the oral pouch and is often lost or entirely 

 overlooked. It has little or no function in locomotion. 



The tentacle (fig. KK, 3, tent.) is the most prominent organ of Noctiluca. It arises from 

 the posterior end of the sulcus as a slender process of nearly uniform diameter, from 0.5 to 0.2 

 the diameter of the body in length. Its diameter is about 0.24 its total length and is sliglitly 

 increased towards the base. Its distal end is bluntly rounded. It is not cylindrical in cross- 

 section, but flattened, with its dorsal surface convex and the ventral one concave, as though the 

 sulcus were continued upon it. Its dorsoventral diameter is about 0.35 its transverse one. It 

 is transversely striate with close-set, evenly spaced protoplasmic net work, especially in its concave 

 or ventral half, which is its contracted side. It is very fragile, easily broken off, and not infre- 

 qiiently missing in living as well as in preserved material. It is thrown in wide undulations in 

 the vertical plane or in a loose spiral coiled anteriorly. These undulations pass distally, and 

 when the tentacle rests upon an obstacle the body is thrust away from it by the action of the 

 tentacle. The undulations tend in some instances to push objects up into the sulcal region. 

 The base of the tentacle passes over into two laterally spreading fibrillar processes which fonn 

 a su])porting framework for the organ attached to the pellicle. 



The cytoplasm is greatly distended by hydrostatic vacuoles in adaption to flotation. It is 

 massed about the nucleus adjacent to the cytostome. This mass sends peripherally to the pellicle 

 slender, branching, and anastomosing strands of protoplasm which unite with a thin network 

 of peripheral cytoplasm. Scattered through the mass of cytoplasm, in the radial strands and 



