80 



Peridiniex 



possibility that the Prorocentracese have been derived from forms similar 

 to Wysotzkia 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 Dinophysese (of Schiitt) may have arisen 

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

 Gymnodiniacese in the Cryptomonads was somewhat different from that 

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

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

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

 consists of two distinct series of forms, the Ceratiese and the Dinophyse*, 

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

 represented in the accompanying table. 



PERIDINIACE^E 



Ceratium 



\ 



Pcridmmm, etc. 



- -i - PHYTODINIACE/E 

 i 



---- 1 --------- 



PROROCENTRACE.'E 



\ 



\ 

 \ 

 \ 



\ 



\' 



GYMNODINIACE^E 



Hemidinium 



/ 

 / 



Polykrikos 



Wysotzkia 



Protochrysis 



CRYPTOMONADINE.E 



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

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

 and in cell-division (excluding the Gymnodiniaceae 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 Peridinieaa 



