380 University of California Publications in Zoology. [Vol.4 



opposite end of the horn from that noted below in C. califor- 

 niense. The prevalence of this renewed growth on the otherwise 

 rugose thecae of the former species is strongly suggestive of a 

 general readjustment of specific surface in this instance by pro- 

 longation of the horns brought about by growth of the regenera- 

 tive type. In figure 30 is shown an instance of regeneration of 

 all three horns after autotoniy which left little of the organism 

 save the midbody. 



31 



lig. 31. — Examples of regenerative growth in distal locations on the 

 horns of Ceratium divaricatum. All from the same plankton collection, 

 X 100. 



In C. calif or )iiense (figs. 31 and 32) I have found one in- 

 stance of proximal growth in the antapicals without preceding 

 autotomy. In this species the tips are closed and the zones of 

 new growth are at the bases of the antapical horns and the old 

 thick-walled antapicals are carried out distally on the intercal- 

 ated new zone. The apical horn on the other hand has a distal 

 zone of new growth of a length corresponding to that which has 

 taken place at the bases of the other two horns. It is obvious 

 that this instance is not one of typical regeneration, for no parts 



