1908] Kofoid. — Exuviation and Autotomy in Ceratium. 355 



condition. This nniforniity of skeletal facies is due to the com- 

 pensatory or assimilative nature of the process of skeletal forma- 

 tion on the newer parts. As a rule a schizont with a rugged, 

 robust, rugose and heavily ribbed ancestral moiety regenerates 

 the lacking part of the thecal wall of a corresponding facies. It 

 is true that schizonts in process of division, or very recently di- 

 vided, will often have the ancestral portion of the theca upon 

 one side of the fission line of a heavy facies, and upon the other 

 side the recently formed part of more or less delicate habit. 

 Such a condition is, however, temporary and Cfuickly disappears, 

 for it is apparent in the members of a chain of schizonts only in 

 those rare instances where two adjacent individuals have been 

 observed during or immediately after division. The remainder 

 of the chain will be in almost all instances of uniformly rugged 

 or delicate habit (fig. 10) according to the facies of the species 

 or local environmental conditions. Evidence at hand indicates 

 that in marine species chain formation takes place in the course 

 of a few hours in the night. The rapidity of division and of re- 

 generation of the lacking skeletal moiety and the compensatory 

 nature of regeneration serve to obliterate to a large extent the dis- 

 tinctions between the skeletal parts of earlier and later forma- 

 tion. We have in this phenomenon a type of compensatory reg- 

 ulation which preserves in the new individuals the balance of 

 skeletal parts and thus provides for normal locomotion and for 

 orientation by gravity. 



5. Occurrence of senile forms in Ceratium. — It seems quite 

 probable that long periods of schizogony may prevail in the ma- 

 rine species of this genus. Sexual reproduction and spore forma- 

 tion are, as yet, Avholly unknown in any marine forms. Zeder- 

 bauer ( :04 and :04a) has observed the former in C. hirundinella, 

 a fresh water species, and spore formation among species in that 

 habitat has long been known. If these types of reproduction 

 occur, as they doubtless do, among the marine forms also, they are 

 certainly elusive and possibly rare. 



Given a long continued period of schizogony accompanied by 

 some degree of assimilative regeneration of the newly formed 

 portions of the theca in the cases of those schizonts which carry 

 respectively the anterior and posterior moieties of the primal 



