KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 41 



This appearance may also be produced by lack of oxygen or other adverse con- 

 ditions consequent on a small supply of fluid under a cover slip durins;: micro- 

 scopical examination. In Peridinitim crassipcs the bright coral red color may 

 be observed in its condensation under the microscope. This will continue until 

 the cytoplasm is colorless and filled with red balls of a considerable size. The 

 addition of fresh sea water to the surrounding medium will, in some cases where 

 the adverse conditions have not killed the organism, result in a diffusion of 

 the color with an ahnost complete disappearance of the red granules in the 

 -cytoplasm. 



In the case of Gyrodinium ocliraceum, recorded above, the condensation and 

 subsequent diffusion of the pigment is evidently not caused by adverse condi- 

 tions in the surrounding mediimi since individuals showing all stages of the 

 process may be found in the same haul. It may be due to physiological condi- 

 tions in the organism itself or to the reacton to stimuli resulting from its own 

 activities or to light, or other factors of its sm-roundings. The relatively rapid 

 changes under the microscope are ^^robably due to the progressive changes 

 taking place in the surrounding medimn. 



The localization of pigments near the girdle, sulcus, longitudinal striae and 

 at the apices is suggestive that internal oxidation processes resulting from 

 contraction, and from other internal responses to stimuli, are potent factors in 

 determining the origin, location, and movements of these products of the living 

 siibstance. 



Surface Differentiation. — The t\T)ical naked dinoflagellate differs but 

 little, if at all, in its ectoplasmic structure from the ordinary flagellate. A 

 differentiated ectoplasm, as distinct from the endoj)lasm, is only rarely met with 

 beyond the production of a thin periplast covering the body. This is thin and 

 elastic and allows for considerable metabolic changes of the body form (fig. A), 

 yet is firm enough to preserve a remarkable sunilarity in shape throughout the 

 individuals of any given species. To such changes some areas of the body are 

 more susceptible than others, as in the antapical region and the posteroventral 

 surface near the sulcus (fig. T). These areas of great susceptibility are un- 

 doubtedly correlated with the function of these portions of the body, the antap- 

 ical region serving as a vent for the ejection of unused or waste material from 

 the body and the sulcus for the ingestion of food. 



The periplast may he marked by lines, ridges or furrows of varying degrees 

 of development. Striae are usuall\' confined to the outermost border of the 

 periplast, but occasionally may be deeper seated and may be indicative of a 

 fundamental organization of the protoplasm, as shown by the linear arrange- 

 ment of pigment (figs. DD, 9, 21). These surface markings are in all cases 

 longitudinal, extending from the girdle to the apices, diminishing in number 

 near the poles and often fading out entirely in the apical regions. Different 

 kinds of surface markings may be present in one species, as furrows and linear 

 lines or dots (fig. W, 3). 



