19081 Kofoid. — Exuviation and Autotomy in Ceratium. 359 



pensatorv character accompanied or preceded this process of 

 exuviation in this individual. 



Another instance of progressive exuviation which is not, how- 

 ever, accompanied by either autotomy or schizogony was noted 

 in C. eugrammum, in a collection taken July 1, 1905, from the 

 surface off San Diego. Dorsal and ventral views of this speci- 

 men are shown in figures 7 and 8. The right half of the theea 

 is composed of delicate hyaline plates, in which the pores are 

 scarcely visible. The left half, on the other hand, is made up of 

 thick, deeply pitted plates. The line between the two contrasted 

 areas is nearly longitudinal and does not follow the oblique fission 

 line, as will be seen on comparison of the theca of this individual 

 with one after normal fission shown in figures 5 and 6. The 

 heavy portion of the exuviating individual contains most of the 

 plates of the anterior moiety of a recent schizont. It lacks, 

 however, apicals 1' and 2' and includes antapicals 1" " and 2" " 

 which belong to the posterior moiety. The hyaline portion of 

 this exuviating individual, which represents approximately the 

 right half of the theca, includes, apicals 1' and 2' which belong to 

 the anterior moiety and lacks antapicals 1" " and 2" ". It seems 

 probable that the senile thecal wall in the right has been exuviated 

 recently and replaced by the new hyaline wall. The distribution 

 of senile plates in both moieties of the theca is conclusive evi- 

 dence that normal schizogony has not occurred in conjunction 

 with this instance of exuviation, but the possibility of an abnor- 

 mally located fission plane is not necessarily excluded. No in- 

 stance of abnormally located fission planes has been observed by 

 me in any Dinoflagellate. A number of other instances of par- 

 tial exuviation were noted in this same collection in C. gaUicum, 

 C. inftexum, and C. carriense, and have since been observed by me 

 in these species in other collections. 



8. Significance of exuviation. — It is obvious that the removal 

 of the heavy senile wall makes possible a restoration of the normal 

 conditions of illumination of the chromatophores and facilitates 

 adjustment of the specific gravity and specific surface to the en- 

 vironmental factors governing flotation. In the collection of 

 plankton in which this exuviating individual was found there 

 was an unusual nnmber of instances of autotomy of the horns in 



