1908] Kofoid. — Exuviation and Autotomy in Ceratium. 377 



the distance from the nucleus at which this reversal of the secre- 

 tion process to one of resolution takes place. A suggestive paral- 

 lel to this phenomenon is seen in the reversal of heliotropism of 

 pelagic organisms by change in temperature described by Loeb 

 (•93). 



III. Eegenkeation in Ceratium. 



1. After schizogony. In normal schizogony the naked por- 

 tion of each segment is immediately covered by a duplication of 

 that part of the ancestral thecal wall passed to its sister sehizont. 



27 



Fig. 27. — Ventral view of Crruiiniii ostenfeldi (?) anil dorsal of C. 

 intermedium showing proportional regeneration of all three horns presumab- 

 ly after autotomy. X 155. 



When it first appears this newly formed wall is an exceedingly 

 thin, structureless film which, liy a process of thickening- and 

 superficial differentiation, rapidly takes on a facies similar to 

 that of the inherited part of the thcca. In all essential par- 

 ticulars this process is similar to the form regulation that attends 

 the fission of other protozoa or of a planarian, but, owiii^' to the 

 considerable differentiation of the skeletal parts and the retention 

 of half the ancestral skeleton, the resemblance to the process of 

 regeneration of lost parts is the more striking. 



2. Regeneration after autotomy, or independently of it. 

 Autotomy is accompanied in this genus by the capacity for re- 



