70 PeridiniedB 



divisions the organism is in the ' (tywwoefcrottro-stage, ' and curious states can be 

 observed before the complete separation of the daughter-cells (fig. 51 # and L). 

 Thus, in Peridinium anglicum, a species which attains its maximum vege- 

 tative activity in the early spring and then rapidly disappears, the formation 

 of these thin-walled non-resting 'cysts,' with the resulting divisions both 

 in the non-motile and motile states, provides a means of very rapid 



multiplication. 



Multiplication by cell-division frequently results in chains of individuals 

 in the genus Ceratium. Such chains have been studied by many investi- 

 gators, but notably by Kofoid ('09 c), who has supplied the most detailed 

 account of chain-formation and has shown that sometimes the chains are 

 heteromorphic in character. He states that 'the morphology of chain- 



Fig. 50. Peridinium aciculiferum Lemm. A, ventral view; B, dorsal view; C, thick-walled 

 resting-spore ; D F, thin-walled resting-spores ; G, division of cell in encysted state. 

 All x500. 



formation is correlated with the presence of an apical pore at the end of an 

 apical horn. As the new skeletal moieties are formed respectively on the 

 posterior and anterior regions of the diverging schizonts, the plasma of 

 the posterior member is drawn out in a long strand which becomes the 

 apical horn. Its tip rests immediately upon the distal end of the newly 

 forming girdle, at which point the plasma of the two individuals remains 

 in continuity without interference by the forming skeleton. As the newly 

 forming skeletons are completed, the apical pore of the posterior schizont 

 is set under the anterior shelf or list of the distal end of the girdle at the 

 margin of the ventral plate of the anterior schizont. The posterior list of 

 the girdle is not formed at this point, and the apical horn as it passes 

 posteriorly lies in a channel or depression on the ventral face of the mid- 

 body along the right margin of the ventral plate.' Kofoid designates the 



