KOFOID AND SWEZY: UNARMOREU DINOFLAGELLATA 39 



red and black colors, the advance being shown in the increasing specialization 

 of the ocellus, sulcus, and girdle. In the genus Pouchetia the species displacing 

 some tones of red, as P. com pacta, P. voracis, P. ruhescens (pi. 8, figs. 89, 90), 

 and P. maculota, with the grouj) of purplish species, P. purpurata, P. purpur- 

 escens, and P. schuetti, are its most highly specialized members, as shown in 

 the degree of integration of the ocellus and the complexity of the girdle and 

 sulcus. 



A few exceptions to this general tendency may be found, as in P. violescens 

 (pi. 11, fig. 118) and P. jnno, which are also highly specialized species in struc- 

 ture, though not in color. A few exceptions also may be found in the other 

 genera. The preponderance of evidence, however, suggests that these lines of 

 structural evolution are, in the main, correlated with progressive movement in 

 coloration towards the red end of the spectrum throughout the larger groups 

 of the Gjonnodinioidae. 



The fresh-water species of the group, confined to the genera Amphidinmm, 

 GjimnodiniHm, and Gijrodinium, are markedly less brilliant in their color than 

 are the pelagic forms. They are colorless, as in Gymnodinium helveticum and 

 Giirodinium InjaliiiHttt, or with dull green or yellow ochre chromatophores, as 

 in most of the other species found in that habitat. The only apparent exception 

 to this conclusion is found in the presence of a minute red eyespot in the mid- 

 venti'al sulcal area. This may be homologous witli the pigment formation 

 common in the pelagic species, but not Avith the ocellus as a whole, though it 

 may be represented in the red core of the latter organ. It is rather a structure 

 comparable to the eyespot or stigma of Euglcna and other fresh-water flagellates. 



Pigment in some form is common in many of the members of the G}inno- 

 dinioidae, and frequently becomes the most conspicuous feature of the organism, 

 as in Gijmnodinium Jincopnnicum (pi. 6, fig. 65), with its markedly motile 

 pomegranate purple pigment. This pigment, as frequently seen in other species 

 also, is almost constantly changing its position imder apparently normal condi- 

 tions, with the organism still active and no indications of the approach of 

 cytolysis. So constantly was this change taking jilace in the individual shown 

 in plate 6, figure 65, that a complete camera sketch of its appearance at one 

 time could not be obtained. 



A more striking instance of the motility of pigment in these forms is show^n 

 in Gyrodininm ochraccuni (pi. 7, figs. 76, 82). In examining a number of 

 individuals of this species a great difference was noted in the pigment formation 

 among them. In some specimens the pigment w^ould be diffused uniformly 

 throughout the body in minute grains. In others these w^ould be localized into 

 larger granules, as in figure 76. Still others would exhiliit various stages be- 

 tween that condition and the band of pigment wound spirally about the body 

 (pi. 7, fig. 82). These appearances were puzzling in the extreme. It was not, 

 however, until a single individual was held under observation for a considerable 

 length of time that an explanation was found. 



