KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 11 



Motor Orgaxelles. — The most important structures of the protozoan organ- 

 ism, from a systematic point of view, are its motor organelles. In tlie Flagellata 

 these consist of flagelhi and vary in number and position in the different groi;ps. 

 The dinofiagellates are characterized by the presence of but two fiagella of 

 different tn^es, transverse and longitudinal, each having its own definitely 

 located position, and, in the case of the transverse fiagellum, a structure peculiar 

 to this group. The longitudinal fiagellum is threadlike in form, trailing after 

 the body, and held more or less rigidly in position, or waving in broad curves 

 (fig. B. long, ft.) or with intense terminal activity. It arises from the posterior 

 pore (fig. B, post, p.) in the sulcus, in case there are two j^ores, and its proximal 

 part lies in the ventral sulcus (snlc.) near the major axis. The transverse 

 fiagellum (fig. B, fr. ft.), on the other hand, n;ns around the l)ody in a nearly 

 transverse plane, arising from the anterior pore near the proximal end of the 

 girdle (fig. B, (oif. p.) and is often, if not always, ribl)on-like in form; it moves 

 in a close-set spiral, or undulating wave of contraction, and is usually lodged 

 in a deep, encircling groove, wound in a fiat or more or less steep spiral from 

 the left ventral face around dorsally to the right side in a more or less complete 

 girdle of one or even several turns (fig. C). In the Adiniferidae and in a few 

 other isolated cases both fiagella arise from the same pore placed at or near the 

 anterior extremity of the body (fig. R, 7). In the majority of forms the two 

 fiagella arise from two different pores on the ventral surface, and not infre- 

 quently at considerable distances from each other (fig. C, 10). 



The transverse flagelhun itself consists of a deeply staining thread or stoxit 

 fibril, bordered on one side by a comparatively wide, finlike sheet of trans- 

 parent i^rotoplasm or membrane, somewhat greater in length than itself, and 

 thrown into ripples or folds of wider amplitude than the fibril. This is in 

 constant, wavelike motion progressing from the j^roximal end distally. Re- 

 versals in direction have occasionally lieen noted. Tlie fiagellum arises from 

 a large deeply staining blepharoplast situated somewhat below the surface of 

 the body. Accurate eytological investigation of its internal relationships has 

 not thus far been made with any degree of success. 



This fundamental organization of the motor organelles may be obscured 

 in several ways. In the Adiniferidae the girdle and sulcus are not developed 

 (figs. R, 5-7), although the nucleus is of the dinoflagellate type, as are also the 

 two fiagella the form and fimetion of which are strikingly suggestive of those 

 of the dinofiagellates included in the Dinif eridae. They also possess a porulate 

 theca in the tribe Thecatoidae. In Protodiuifer (fig. R, 2) the very faintly 

 developed girdle clearly forecasts the fundamental relationships of this organ 

 found in the remainder of the dinofiagellates. It probably represents the be- 

 ginnings of the development of these peculiar relations within the group. 



In the Diniferidae this fundamental organization is sometimes obscured by 

 the interposition of long encysted stages, with a consequent shortening of the 

 dinoflagellate stage of the life cycle, by secondary loss of the fiagella with the 



