1920] Kofoid: New Interpretation of the Structun of Noctiluca 323 



and extending posteroventrally. Its length is about 0.6 that of the 

 body and its form is that of a rod of uniform caliber with rounded end. 

 It is thrown into curves strikingly similar to those of the tentacle of 

 Noctiluca, but it is not figured a.s striate as it is in Noctiluca. 



The exact point of origin of this tentacle does not appear to be 

 constant in Pouchet's (1885, 1892) figures. In certain ones (1885, 

 pi. 4. fig. 37; 1892, pi. 11, figs. 3, 6, 7) the tentacle arises from the 

 posterior region of the sulcus. In one instance (1892, pi. 11, fig. 2) 

 it arises from the left margin of the sulcus and in another (1892, 

 pi. 11. fig. 4) from the posterior end of the body. In the latter instance 

 the point of origin may be determined by the very evident mobility 

 of the various regions of the body, and may not be a morphological 

 displacement. The point of origin indicated in the former instance 

 represents either an oversight in drawing or a real shifting of the 

 point of origin of the "tentacle" out of the sulcus to the left margin. 

 There may be a single secondary amoeboid projection, or a bilobed one 

 immediately anterior to the base of the tentacle, either of which would 

 be suggestive of the labile condition of the region. Some individuals 

 entirely lack the "tentacle," whether by autotomy or retraction is 

 unknown. If the latter is the case the structure should be called a 

 pseudopodium. The adjacent secondary process suggests the pseudo- 

 podial interpretation, but the form of the major process is clearly 

 tentaculate. 



The cytoplasm of the body is much vacuolated and is aggregated 

 around the nucleus, as in Noctiluca. It is 175 to 200 p in length, has 

 yellow chromatOphores, a complete girdle, and no extension of the 

 sulcus upon the epicone. For these reasons it does not appear to be 

 a developmental phase of Noctiluca, although the tentacle and vacuo- 

 lation are suggestive of it. Its small zoospores are typical Gym- 

 nodinium without tentacle, unlike those described for Noctiluca (pi. 18, 

 figs. 4a, 46 ) , which have at this stage a large tentacle. If the ' ' tentacle 

 is. in reality, only a pseudopodium the species may well remain in 

 Gymnodinium, but if it is a permanent tentacle it should be removed 

 to Pavillardia gen nov. Kofoid and Swezy MSS. 



The second genus of the tribe Gymnodinioidae with tentacle is 

 PaviUardia nov. gen. Kofoid and Swezy MSS, with one species, P. 

 tentaculifera Kofoid and Swezy MSS (fig. H). This has a simple 

 Gymnodinium-Uke body with girdle, sulcus, and the two flagella. The 

 longitudinal flagellum, in the somewhat limited material we have 

 examined, is fully developed but in some instances was not found. 



