KOFOID AND SWEZY: UNAKMORED DINOFLAGELLATA 37 



Those rodlets or rhabdosomes, as they have been called by Schlitt (1895), 

 are constantly present in the different individuals of many species, while in 

 other s]ieeies they may be present in a few individuals and absent in others. 

 With the cytolysis of the liody these rodlets melt away as do the fluid-filled 

 vacuoles, indicating a similarity in their structure. We have, therefore, con- 

 fined the term rhabdosome to those structures which have a greater perma- 

 nency, as in the long slender rhabdosomes constantly present in the genus Toro- 

 diniiim (fig. II), and which do not deliquesce so readily as do the ordinary 

 vacuoles of the cytojilasm. 



The endoplasm is usually visibly granular, but in the genus Erythropsis 

 and in a few species in other genera this granular appearance is lacking, the 

 body presenting a hyaline, almost glassy texture that persists in Erythropsis 

 imtil c_\i:olysis of the body occurs. 



Coloration. — The pelagic dinoflagellates are remarkable for their diversity 

 of coloration and for a brilliancy and delicacy of tone which give to the minute 

 transparent body a beauty that is almost impossible of analysis and equally 

 difficult to reproduce. In comparatively few species is the color confined to a 

 single tint except in those forms having chromatophores or colored pigment. 

 The usual condition shows a background of soft pearl grey shot through with 

 one dominant color, intermingled w^ith broken flashes of one, often two or more, 

 contrasting colors, the entire combination producing a rich effect impossible 

 of adequate reproduction. 



The color may be resident in chromatophores (pi. 1, figs. 1, 4), yellow, 

 yellow ochre or greenish, or in pigment granules (pi. 6, figs. 65, 67, 69), or it may 

 by diffusion be a component part of the cytoplasm itself, with no evidence what- 

 ever of localization in even minute particles (pi. 6, figs. 63, 68). A relatively 

 greater munl)er of thecate forms than naked dinoflagellates possess chromato- 

 phores. In case of naked dinoflagellates the chromatophores are confined to 

 the simpler, more generalized species, namely, Amphidinium (fig. U) and the 

 lower forms of Gymnodinimn (fig. X) and Gyrodinium (fig. CC). In the more 

 highly specialized groups of the Gymnodiniioidae they are almost entirely 

 absent, as in Poiichctin (pi. 11) and Erythropsis (pi. 12). 



Nearly the whole range of colors of the spectrum are to be found within the 

 species of the different members of the Gymnodiniidae. It is noteworthj^ also 

 that a certain amount of correlation may be found in the group between the 

 coloration and the amount of specialization attained within the group. In 

 Amphidinium the predominating colors are green and yellow (pi. 1, figs. 1, 4, 

 11), correlated with a relatively greater number of chromatoi)hore-bearing 

 forms. The colors of the red end of the spectrum are entirely unknown in this 

 genus. 



In the genus Gymnodinium its most specialized species, sucdi as G. pachy- 

 dermatum, G. dogieli, and G. amphora (pi. 3, figs. 32, 34, 26), show a type of 

 differentiation which throws them outside the line of evolution which produces 



