KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 



159 



Organology 



Gymnodinium stands next to Amphldiniiim in its organology, differing 

 mainly from that genus and from Gyrndiuium in tlie position and arrangement 

 of girdle and sulcus. The epicone occupies a relatively greater proportion of 

 the body than in Amphidinium, the girdle being placed nearer the center of the 

 body (fig. V) . A few species, as for example G. amphora (fig. AA, 6), approach 

 the Ampliidinium type. The girdle 

 may form a complete circle around 

 the body, as in G. lineopimicum (fig. 

 X, 17), or the ends may 1)e displaced 

 from a very slight amount up to 

 nearly 0.2 of the total length of the 

 bod}'. A displacement as great as 

 this is rare, G. rubrum alone showing 

 it (fig. Y, 4). When so displaced 

 the girdle approaches the Gyrodiniiim 

 type. It is usually submedian or 

 slightl_v anterior in position. Three 

 species only exhibit, in a noticeable 

 degree, a location of the girdle pos- 

 terior to the equator or middle of the 

 body, G. dissimile, G. inusei, and G. 

 vor'ticella (figs. X, 32, 3, 29). 



The sulcus is usually well devel- 

 oped, without torsion or with only a 

 very slight amount, as in G. ruhrum. 

 It usually extends from or near the 

 apex to the antapex in a more or less 

 sinuous line. It is shallow anteriorly, 

 generally deepening posteriorly, its 

 greater development in the latter re- 

 spect being reached in G. bifurcatum, where the sulcus bifurcates nearly the 

 entire length of the hj^ocone (fig. A A, 3). Its borders are not so protuberant 

 as in AmpJiidinium, yet are apparently ca]3able of great distension, as shown by 

 the size of the food bodies sometimes ingested (pi. 6, fig. 65). 



The position of the nucleus is not constant, but it may be found in any part 

 of the body. This sometimes happens within the species, as in G. lieterostriatum, 

 as a result of the ingestion of large food masses which displace the existing cell 

 contents. In the greater number of species it is found in the central or posterior 

 parts of the bod,v. It usually has distinct, beaded chromatin threads. One 

 species only, G. ruhrum (pi. 8, fig. 86), shows a wvU develoj^ed, perinuclear 

 membrane. This is simihir in its structure to that found in Gyrodinimn coral- 

 linum (pi. 10, fig. 117). It is noteworthy also tliat tliis species stands nearest 

 to G yrodinium in its type of girdle arrangement. 



post. p. 



long. fl. 



Fig. V. Gymiwdlnium dotjieli sp. nov. Abbrevia- 

 tions: ant. p., anterior flagellar pore; ect., ectoplasm; 

 cpi., ejiioone; gir., girdle; hyp., hypocone; long, fl., longi- 

 tudinal flagellum; n., nucleus; post, p., posterior pore; 

 pus., pusule; rcf. gr., refractive granules; rod., rodlets; 

 sulc, sulcus; tr. fl, transverse flagellum; vac, vacuoles. 

 X 500. 



