Phytodiniaceae 57 



in all cases it is located in a concentration of the cytoplasm from which 

 numerous protoplasmic strands stretch out through the large vacuole which 

 occupies the greater part of the interior of the cell. Numerous small, oval 

 chromatophores give the cells a brown or golden-brown colour. There is also 

 an abundance of small oil globules, and larger refractive amylum-bodies, the 

 latter sometimes almost filling the whole cell. The normal vegetative condition 

 in the Pyrocystaceae appears to combine features usually exhibited by the 

 resting and the encysted states of other Peridiniece. The cell possesses the 

 thick cell-wall characteristic of the resting-state, but undergoes repeated 

 divisions such as occur in the more usual encysted condition. 



The systematic position was discussed by Blackman ('02), who stated that 

 ' but for the somewhat meagre evidence provided by these figures of Schtitt, 

 the Pyrocysteee would have to be considered as an algal group of quite 

 unknown affinities.' The flagellated spores observed by Schtitt (in ' Pyrocystis 

 lunula ') were of the Gymnodiniuni-type, with a transverse furrow, and it 

 was for this reason that he placed the Pyrocystege in the Gymnodiniaceas. 

 It is, however, the recent investigations of Apstein ('06) and Dogiel ('06) 

 which have furnished the strongest evidence of the Peridinian nature of the 

 Pyrocystacese. Even though the old 'Pyrocystis lunula' has been transferred 

 to the Gymnodiniacese as Diplodinium lunula, yet its encysted states present 

 no essential differences from the cells of Pyrocystis. In both cases the walls 

 are of cellulose, the nucleus is large, there are numerous yellow-brown 

 chromatophores, and oil-globules and amylum bodies are found to be the 

 food-reserves. Since Diplodinium lunula is now definitely known to form 

 small Gynmodinium-\ike flagellated cells in one stage of its life-history, it is 

 not unreasonable to suppose that species of Pyrocystis are closely allied 

 organisms in which the encysted state has become the normal vegetative 

 phase and the motile state has been suppressed. 



Family Phytodiniacese [Klebs in part]. 



Klebs ('12) established this family of the Peritliniese to include four newly described 

 genera (Pkytodinium, Tetradinium, Stylodinium and Cflceodinium) and the genus Pyrocystis. 

 Since, however, the relationships between these new genera are not at all clear, and their 

 affinities with Pyrocystis are possibly somewhat remote, the present author prefers to 

 retain Pyroci/stis in the separate family Pyrocystacese (as above). All the new genera 

 described by Klebs include comparatively small fresh-water forms, whereas Pyrocystis is 

 a genus of much larger marine forms in which all the species are luminous. It is probable 

 that the phylogenetic history of Pyrocystis is very different from that of Phytodinium, 

 Tetradinium, etc. Until more observations have been made, or further allied forms 

 discovered, it is difficult to discuss the new genera proposed by Klebs. For instance, 

 Tetradinium javanicum Klebs is so like the encysted state of certain fresh-water species 

 of Ceratium that one may be forgiven for suggesting that there is, as yet, no absolute 

 proof that it is not such a state, especially in view of the fact that divisions ni;iy occur in 

 cysts of the Peridiniacea; with the formation of new cysts (G. S. W. 'OOj. It may, of 



