KOFOID AND SWEZY: UNARMORED DINOPLAGELLATA 13 



Two other functional jDossibilities of this prod remain. The prod may be 

 either a feeding or a defensive structure. The energetic retractions combined 

 with the capitate end of the tentacle would tend to press any object against 

 the ventral furrow if caiight between it and the body on its anterior face. 

 Erjjfhropsis exfrudens has no chromatophores. No food bodies were noted in 

 the individuals observed. ]\Iany if not all Pouchetia, Coclilodiniiim, and 

 Gyrodiniiim are holozoic. Holozoic nutrition is indicated for this species also 

 and the tentacle might be effective as an organ of ingestion. 



Observational evidence is likewise lacking for the second function suggested 

 above, namely, that of an organ of defense. In fact in all our observations on 

 living holozoic Gymnodinioidae no instance of active capture and ingestion of 

 food has been seen. It is obvious, however, from the size and activities of this 

 tentacle that a marauding holozoic dinoflagellate, such as a Pouchetia, CocMo- 

 diuiiDH, or the larger Polijkrikos, or even Noctiluca, would find it rather difficult 

 to capture, hold, and engulf a vigorously kicking Erytliropsis. The function 

 of the tentacle as an organ of defense is not incompatible with that of the 

 capture of food, although the operation in either fashion involves contradictory 

 internal states on the part of the organism, conditioned by hunger and satiety 

 or by the nature of its contact with other organisms. 



Another type of structure, the value of which as a motor organelle in these 

 forms is problematical, is the peculiar form of pseudopod formation which has 

 been described by Zacharias (1899) for a chromatophore-liearing Gi/»iiiodi)n'i(m, 

 G. zachariasi (fig. BB, 3). This has been cited by West (1916) as indicative 

 of holozoic nutrition, but Zacharias offers no evidence that these structures are 

 used in the capture of food or as motor organelles. They are outgrowths of 

 the extremely plastic sulcal area, modifications of which are found in Cochlo- 

 diuium, and Pouchetia, culminating in the i^rod of Eri/thropsis (fig. SS). The 

 loss of the longitudinal flagellum in those forms in which the prod or tentacle 

 is well developed might indicate that its function is, to some extent at least, sub- 

 served by the new organelles thus introduced. Evidence on this point, however, 

 is lacking. Such retractile processes are not unlike those recorded by Rhodes 

 (1920) for the holozoic poh^nastig•ote flagellate, Collodictyon. Similar 

 pseudopodia-like processes are functional in this genus in capturing organisms 

 for food. 



Furrows and Torsion of the Body.— Closely connected with the motor 

 organelles, l)oth morphologically and in their evolutionary development, and 

 equally important from a systematic point of view, are the furrows of the body 

 of the dinoflagellate. They constitute its most striking structural features. 

 All stages of development and elaboration of these peculiar and characteristic 

 structures are found within existing species of the group, from the fine, faint 

 traces in the lower forms to the sj^iral of three or four turns in the more special- 

 ized Cochlodiuium, and to the elaborate furrows outlined by lists or fins of great 

 beauty and delicacy of design in the thecate forms of Gonyaulax, Peridinium, 



