384 University of California Puhlications in Zoology. [Vol. 4 



generation of the newly forming part of the exoskeleton occurs. 

 Skeletons of senile facies may be removed by exuviation, plate 

 by plate, often at the time of schizogony. This exuviation makes 

 possible readjustments of specific gravity and specific surface to 

 changing conditions of flotation. 



Autotomy of the two antapicals, or of all three horns is of 

 widespread occurrence among many species of Ceratium. It is 

 more abundant in collections from deeper levels than in those 

 fi'om the surface. It is caused by local resolution of the cellulose 

 wall and is regulatory in character, preserving in the horns after 

 autoton)y the proportions characteristic of the species. Auto- 

 tomy assists in the adjustment of specific surface and possibly 

 also of specific gravity to changing conditions of flotation, espe- 

 cially as affected by temperature. 



Regeneration of the horns with or without preceding auto- 

 tomy may occur in all three horns. It is also regulatory in 

 character and tends to preserve the norm of the species. 



