352 University of California Publications in Zoology. [Vol. 4 



whose habit is strongly suggestive of a senile condition and whose 

 cell wall is apparently thickened by the accretions of long-con- 

 tinned growth. Obviously such structure must profoundly affect 

 both metabolism and flotation, for it cuts down the access of light 

 to the chromatophores of the cell on the one hand and on the other 

 aft'ects both specific gravity and specific surface. 



3. Transfer of the ancestral theca in schizogony. — Asexual 

 reproduction in Ceratium as in most Dinoflagellates and the flag- 

 ellates generally, is accomplished by binary fission, though the 



Fig. 9. — Dorsal view of Ceratium vultur, a form with short horns in 

 chain showing compensatory character of newly formed thecal moieties, to 

 wit, the two thecal halves between the dotted fission lines. The weight of 

 the lines represents the relative thickness of the walls. X 220. 



possibility of multiple spore formation can not be excluded. In 

 the binary fission of Ceratium, as has been shown in detail by 

 Lauterborn ('95) for C. hirundinella, and as may be seen in 

 most recent schizonts (figs. 5 find 6), the plane of fission is not 

 transverse but passes obliquely across the body from the right 

 anterior to the left posterior margin, separating the parental 

 theca into two parts. The anterior part includes the apical horn 

 and precingular plates 1" and 2".^ and postcingular plates 1' ", 

 2' " and 3' " with the left half of the girdle which is included 

 between the two series of plates. On the dorsal face the suture 



