318 University of California Publications in Zoology ["Vol.19 



Although the essential elements in the structure of Nobtiluca, in 

 the typical large, unicellular phase commonly found in the neritic 

 plankton, have long been known, and are figured more or less imper- 

 fectly by the earlier investigators of this unique animal, there are in 

 the literature no comparative morphological analyses and correlations 

 of these structures with those of any dinotlagellate. The grounds 

 upon which Jollos (1910) proposed the inclusion of the Cystoflagellata 

 (NoctUuca) in the Dinoflagellata are very general ones, including the 

 resemblances in nuclear structure and mitosis, the presence of a 

 tentacle, as in Erythropsis, and the inflated sphere of Pyrocystis 

 (Gymnodiniwm) lunula with its local aggregation of the cytoplasm. 

 Most stress, however, is laid upon the swarm spores of NoctUuca as 

 being indicative of dinotlagellate affinities. Beyond these elemental 

 resemblances Jollos does not develop the homologies, and concludes by 

 placing the Cystoflagellata in the Dinoflagellata as an order coordinate 

 with the "Peridineen. " within which he includes all those organisms 

 previously allocated in the Dinoflagellata. In these allocations he is 

 followed by Poche (1913) in his System der Protozoen, but Poche gives 

 no elaboration of the basis of such allocation. In making this alloca- 

 tion these authors have adopted a view earlier proposed but not fol- 

 lowed by Biitschli (1885). 



Data brought to light by a monographic investigation, now in 

 press, of the unarmored Dinoflagellata of the San Diego region, by 

 the writer and Dr. Olive Swezy. make possible a reconsideration of 

 the morphology of NoctUuca and a detailed homologizing of its essen- 

 tial structures with those of the simple, typical, naked dinotlagellate, 

 and with those of some recently discovered, more highly specialized, 

 tentaeulate forms of the Dinoflagellata. 



The mononucleate, vegetative, free, and active stage of NoctUuca, 

 comparable with the usual unencysted free stage of dinoflagellates, has 

 certain structural features noted in a fragmentary fashion by various 

 earlier writers on the morphology of this animal. These I have 

 recently verified on living and preserved NoctUuca from San Fran- 

 cisco Bay. and present herewith carefully oriented figures, and a new 

 analysis and homology of these structures with the organs of the 

 Dinoflagellata. 



These features (pi. 18, figs. 1-6) are (1) a deep groove on the 

 ventral face at one end of which is found (2) the transversely striate 

 tentacle. This groove is continued at the opposite end in (3) a 

 straight, narrow prolongation, which in small individuals consider- 





