1908] Kofoid. — Exuviation and Autotomy in Ceratium. 351 



structureless, minutely porulate type seen in C. trichoceros (fig. 

 16) to the thiek-walled, much ribbed and coarsely porulate one 

 exemplified in C. robicstum and C. limulns. In the normal course 

 of asexual reproduction the type of wall characteristic of the 

 species is maintained by immediate and rapid regeneration of 



■ - ap, p. 



V. pi. 



r. ant... 



Fig. 7. — Ventral view of another individual after exuviation of part of 

 the thecal plates. Senile theca « ith heavy sutures and pores. X 880. 

 Fig. 8. — Dorsal view of same. X 880. 



(For explanation of abbreviations, see under figures 5 and 6.) 



the new half of each skeleton at the time of schizogony. The 

 differences between the newer and older thecal moieties of indi- 

 viduals recently divided and still in chain are usually obliterated 

 by assimilative regeneration before the separation of the schi- 

 zonts. On the other hand, within the limits of each species there 

 is a rather wide range of wall structure between the more delicate 

 and the more robust habits, which appears to be correlated with 

 environmental conditions especially those affecting flotation. Oc- 

 casionally heavily armored individuals of a species are found 



