132 



PROTOZOA 



S 



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and fresh-waters. Gymnodinium pulvisculus is sometimes parasitic 

 in Appendicularia (Vol. VII. p. 68). Polykrikos 1 has four trans- 

 verse grooves, each with its nagellum, besides the terminal one. 



Many of the marine species 

 are phosphorescent, and play 

 a large part in the luminosity 

 of the sea, and some give it 

 a red colour. 



Several fossil forms have 

 been described. Peridinium 

 is certainly found fossil in 

 the firestone of Delitzet, be- 

 longing to the Cretaceous. A 

 full monograph of the group 

 under the name " Peridi- 

 niales " was published by 

 Schiitt. 2 



The Cystoflagellates con- 

 tain only two genera, 3 Nocti- 

 luca, common at the surface 

 of tranquil seas, to which, 

 as its name implies, it gives 

 phosphorescence, and Lepto- 

 discus, found by K. Hert- 

 wig in the Mediterranean. 

 Noctiluca is enormous for a 

 Flagellate, for with the form of 

 a miniature melon it measures 



Fig. 47. Pyrocystis fusiformis, Murray, 

 x 100. From the surface in the Guinea 

 Current. (From Wyville Thomson.) 



about 1 mm. (--$ ) or more in 



diameter. In the depression 



is the "oral cleft," from one 



end of which rises, by a broad base, a large coarse flagellum, 



as long as the body or longer and transversely striated. In 



front of the base of the 



flagellum 



are 



two lip-like promin 



1 According to Bergh, Polykrikos lias as many nuclei as grooves, each accompanied 

 by one or more "micronuclei." Possibly these latter bodies are merely blepharoplasts, 

 in connexion with the transverse flagella. 



2 Engler and Prantl's Pfianzenfamilicn, 1. Teil, Abt. 1, 1896. 



3 The luminous genus, Pyrocystis (Fig. 47), regarded as a Cystoflagellate by 

 Wyville Thomson, has a cellulose wall, no mouth, and in the zoospore state has 

 the two flagella in longitudinal and transverse grooves of the Dinoflagellata. 



