322 University of California Publications in Zoology [Vol. 19 



other flagellates. The sulcus is, therefore, not only an organ of great 

 lability in the speciation of the Dinoflagellata but may also be very 

 mobile in the individual. 



It is likewise from the margins of this region that the pseudopodia 

 and in higher genera the tentacles of the Dinoflagellata are developed; 

 and it is this development of these outgrowths of the sulcal region in 

 otherwise typical Dinoflagellata that affords one of the grounds for the 

 dinoflagellate affinities of Noctiluca. 



The lability of the eytostomal area in Collodictyon triciliatum, a 

 polymastigote flagellate, has recently been demonstrated by Rhodes 

 (1919), who figures the formation of temporary pseudopodia from 

 the sulcus of this polymastigote flagellate, which are used in the 

 capture of organisms for food. 



Among the dinoflagellate,s there is but one instance (fig. C) of 

 pseudopodia so designated on record, that of Zacharias (1899) who 

 found such structures in Gymnodinium pdlustre (later called G. 

 zachariasi by Lemmerman, 1900). The protoplasmic protrusions of 

 this species take the form of simple hyaline, tenacle-like, or branching 

 outgrowths from the sulcus or its immediate margin adjacent to the 

 flagellar pore. No use of these processes in the capture of food was 

 noted, but the conjecture was made by Zacharias that they were 

 utilized in rapid saprophytic nutrition prior to encystment. It is 

 quite possible that they are in reality degenerative phenomena. Ex- 

 trusions of plasma from the flagellar pores of thecate forms as cytolysis 

 approaches is rather a common phenomena in our experience. 



There are four genera thus far known among Dinoflagellata in which 

 a distinct tenacle is formed from the margin of the sulcus. These 

 are Gymnodinium pseudonoctiluca Pouchet (1885), Pavillardia tenta- 

 culifera Kofoid and Swezy MSS, Proterythropsis crassicaudata Kofoid 

 and Swezy MSS, and Erythropsis agilis Hertwig (1884). The evolu- 

 tion of tentaculate species among the Dinoflagellata appears to have 

 taken place independently in different genera, and not in a single 

 series of species within a single genus. The addition of Noctiluca to 

 the series of tentaculate Dinoflagellata therefore accords with the con- 

 ditions known to prevail in that subclass. 



In Gymnodinium pseudonoctiluca Pouchet (1885, 1892), we have 

 a species with the typical morphology of Gymnodinium (fig. D), with 

 girdle of one turn, straight sulcus, transverse flagellum in the girdle, 

 and trailing posterior flagellum. In addition to these two flagella 

 there is a "tentacle" originating in the posterior region of the sulcus 





