Phylum Pyrrhophyta [ 101 



the protoplasm in the cysts is seen to become luminous in response to disturbance of 

 the medium; they are among the agents of phosphorescence at sea. In Gymnodinium 

 Lunula the protoplast of each large globular cyst undergoes division into several 

 protoplasts which do not immediately become flagellate; each of them becomes 

 crescent-shaped, deposits a cell wall, and is released by dissolution of the wall of the 

 parent cyst. In the crescent-shaped cysts, the protoplasts divide into several which 

 develop flagella and escape as typical gymnodinioid cells. 



In Hemidinium the girdle forms less than a complete circle; in Amphidinium, the 

 girdle is close to the anterior end of the cell; in Gyrodinium, it forms a steep left 

 spiral; in Cochliodinium it forms a left spiral of more than one and one half turns. 



Family 3. Dinamoebidina nom. nov. Order Rhizodiniales and family Amoehodi- 

 niaceae Pascher (1931), not based on generic names. Non-pigmented amoeboid 

 organisms producing crescent-shaped cysts which germinate by releasing gymnodini- 

 oid zoospores. Dinamoebidium varians Pascher (1916; originally Dinamoeba, but 

 there is an earlier genus of this name, and the author changed it). 



Family 4. Polykrikida [Polykrikidae] Kofoid and Swezy in Mem. Univ. California 

 5: 395 (1921). Family Polydinida Butschli (1885), not based on a generic name. 

 There is a single genus Polykrikos, of only three known species. They are colorless 

 predatory organisms of such a structure as might be produced if a cell of Gymnodi- 

 nium were repeatedly to enter upon division and fail to complete it. Each elongate 

 cell bears a single extended sulcus and a series of girdles; with each girdle are asso- 

 ciated the usual two differentiated flagella. Of nuclei there are usually half as many 

 as of girdles. The cells contain structures called nematocysts, whose development 

 and structure was studied by Chatton (1914). Each nematocyst consists of a conical 

 wall, with a peculiar operculum at the broad end, surrounding a minute cavity 

 containing fluid and a coiled thread. Nematocysts are supposed to be homologous 

 with trichocysts, and to contribute to protection, or to the capture of prey; the points 

 seem not fully established. They occur only in this family and the following. 



Family 5. Pouchetiida [Pouchetiidae] Kofoid and Swezy in Mem. Univ. of Cali- 

 fcrnia 5: 414 (1921). Each of the gymnodinioid cells contains a light-sensitive ap- 

 paratus, the ocellus, consisting of a pigmented area and of one or more transparent 

 globes, of unknown composition, serving as lenses. Most species have nematocysts. 

 Protopsis, Pouchetia, etc.; Erythropsis, in warm seas, with a prominent tentacle. 



Family 6. Protodiniferida [Protodiniferidae] Kofoid and Swezy in Mem. Univ. 

 California 5:111 (1921). Family Pronoctilucidae Lebour Dinofl. Northern Seas 10 

 (1925). Predatory organisms, the cells subglobular, without ocellus or nematocysts, 

 but with a tentacle. Pronoctiluca Fabre-Domergue 1889 {Protodinifer Kofoid and 

 Swezy 1921); 0.v}'rr/iw Dujardin. 



Description of the neuromotor apparatus and process of division in Oxyrrhis 

 marina by Hall (1925) provides part of the authority for, and is in good conformity 

 to, the remarks on mitosis included above in the description of the phylum. The 

 nucleus contains a prominent internal body (endosome) which does not contain the 

 material of the chromosomes and does not disappear during mitosis. A centrosome, 

 close outside the nuclear membrane, is connected by two rhizoplasts to blepharo- 

 plasts at the bases of the flagella. When a cell is to divide, the centrosome divides; 

 the daughter centrosomes do not necessarily lie at the poles of the nucleus where 

 the chromosomes assemble. Each daughter centrosome appears to generate one 

 rhizoplast, blepharoplast, and flagellum to complete the neuromotor apparatus of a 

 eel]. In due course, the endosome, nucleus, and cell undergo constriction. 



