1908] Kofoid. — Exuviation and Autotomy in Ceratium. 349 



of Gonyaulax unequivocal evidence of typical oblique fission of 

 the theca in recent schizonts. In the genus Ceratium obliqu.3 

 fission of the theca or exoskeleton universally attends schizogony 

 and the parental theca is shared by the daughter schizonts. More- 

 over in this genus no instance of total ecdysis has been noted in 

 any of the numerous collections of living and preserved plankton 

 which I have examined, neither from the crowded swarms in the 

 "red water" or in condensed plankton collections which have 

 stood in the laboratory for several hours. Fission of the theca 

 in schizogony and entire absence of total simultaneous ecdysis 

 thus appear to be the rule in the genus Ceratium. The possibil- 

 ity of the occurrence, however, of total ecdysis at the time of 

 sexual reproduction must not be excluded. 



Exuviation. 



1. Statement of the prohle)n. — It becomes, therefore, a mat- 

 ter of interest to consider the formation of the cell wall and the 

 method by which the ancestral theca is passed on in asexual 

 reproduction and what means, if any, exist for ridding the organ- 

 ism of the accumulating products of metabolism found in the cell 

 wall, and of adapting these fixed skeletal structures to the chang- 

 ing environmental conditions which affect profoundly the capac- 

 ity of the organism for flotation and maintenance in its position 

 within the zone of optimum illumination in the upper levels of 

 the sea. 



2. Structure of the cell wall. — It is not my purpose to discuss 

 the details of this subject which has been elaborately worked out 

 by Schiitt ('95, '99, and :()0) but merely to call attention here 

 to the facts pertinent to this discussion. The wall and its super- 

 ficial modifications are formed of cellulose or of a substance close- 

 ly allied to it, and the material is laid down on the periphery of 

 the main mass of the cell plasma and its extensions in the apical 

 and antapieal horns. Its increase in thickne&s is brought about 

 probably b}' appositional rather than intussceptional growth, cen- 

 tripetally on the inner, and centrifugally on the outer face of the 

 wall, but principally by the latter process. Access to the outer 

 face of the wall is gained through the many pores which are dis- 

 tributed in the wall in all regions, though more sparsely towards 



