1908] Kofoid. — Exuviation and Antotomy in C'eratium. 353 



line crosses the girdle near the mid-dorsal line (fig. 6) but on the 

 ventral face Laiiterborn figures it as passing along the anterior 

 margin of the ventral plate at the base of the apicals and down 

 to the flagellar pore along the right margin of precingnlar 1' " 

 and thence through the longitudinal furrow along the right 

 margin of postcingular 1' " to the postcingular suture. Its 

 course is outlined by a dotted line in figures 4 and 5. The pos- 

 terior schizont receives the remainder of the plates, precingulars 

 3" and 4", postcingulars 4' " and 5' ", antapicals 1" " and 2'' '' 

 and the other half of the girdle plates as well as the ventral plate 

 (Lauterborn '95). The right and left antapical horns thus be- 

 long to the posterior schizont. and the apical to the anterior one. 



At the completion of each schizogony the parental theca is 

 shared in this manner between the two schizonts, each of which 

 regenerates during the process the missing half of the thecal 

 exoskeleton. In chain formation (figs. 9 and 10) which ensues 

 when schizogony is rapidly repeated the two parts of the ancestral 

 theca are found respectively upon the anterior and posterior 

 schizonts of the chain. It is evident that these ancestral por- 

 tions may continue to form a part of the armor of some two of 

 the offspring for an indefinite time unless some other type of 

 reproduction intervenes, such as spore formation or conjugation, 

 in which the cell contents abandon permanently the thecal exo- 

 skeleton of this vegetative period, or unless some modification 

 of the usual physiological processes occurs by virtue of which the 

 thecal wall is resolved or shed in whole or in part. 



4. Assimilative regeneration of the theca in schizogony. — It 

 might be supposed that these ancestral contributions could be de- 

 tected readily by their senile characters, such as thickened wall, 

 and excessive development of superficial ribs and lists and in- 

 creased depth of color. l)ut this does not appear to be the case. 

 In many instances of chain formation which I have observed 

 among various species of this genus I have yet to find an instance 

 in which the older and newer portions of the thecae of the an- 

 tei'ioi- and posterior schizonts of a chain showed any considerable 

 difference in their structural characters sua'gestive of a senile 



il have elsewhere (:07) desi-ribed tlie thecal plates of Ceratium and 

 proposed the nomenclature here employed. 



