80 



Peridimese 



possibility that the Prorocentracese have been derived from forms similar 

 to Wysotekia and allied genera; and there is much to be said in favour of 

 Pascher's suggestion that some members of the Gymnodiniacese may have 

 originated from Cryptomonads not far removed from Protochrysis Ph&o- 

 phycearum. It is also possible, as suggested by Bergh, and further 

 emphasized by Klebs, that the Dinophyseae (of Schiitt) may have arisen 

 from the Prorocentraceaa. Since it is not improbable that the origin of the 

 Gymnodiniacese in the Cryptomonads was somewhat different from that 

 of the Prorocentracese, and as there is no doubt that from the Gymnodiniacese 

 the characteristic group of the Ceratiese has arisen through such forms as 

 Glenodinium, it is quite likely that the Peridiniaceas as at present understood 

 consists of two distinct series of forms, the CeratieaB and the Dinophysese, 

 and is therefore diphyletic. The possible evolution of the Peridinieae is 

 represented in the accompanying table. 



PERIDINIACE.E 



CERATIE^ ? | 



DINOPHYSE^E 



Ceratium 



Peridinium, etc. 



Glenodinium 



- PHYTODINIACE.E 



P-4 



I I 



| / PYROCYSTACE.E 



I / 



PROROCENTRACESE 



V 



I 



I 

 GYMNODINIACE.E 



Hemidinium 



Polykrikos 



Wysotzkia 



Protochrysis 



CRYPTOMONADINE^: 



It is quite possible that the Bacillarieaa are remotely related to the 

 Peridiniea?. In both groups the cell-wall is composed of two distinct halves, 

 and in cell-division (excluding the GymnodiniaceaB and certain other low 

 types) each daughter-cell must acquire a new half- wall. The pigment of the 

 chromatophores is similar, and the food-reserves are the same in each case. 

 On the other hand, the longitudinal furrow with its flagellar pore, through 

 which the two flagella pass, indicates that the locomotion of the Peridiniese 



