No. 13. — Reports of the Scientific Results of the Expedition to the 

 Eastern Tropical Pacific, in charge of Alexander Agassiz, hy the 

 U. S. Fish Commission Steamer "Albatross" from October, 

 1904, to March, 1905, Lieut. Commander L. M. Garrett. 

 U. S. N., commanding. 



XX. 



Mutations in Ceratium. By Charles Atwood Kofoid. 



CONTENTS. 



Normal schizogony in Ceratium . 213 



Division of ancestral skeleton . 214 

 Formation of new skeletal 



parts 214 



Similarity of normal schizonts 



in chain . 215 



The genus Ceratium 217 



Tripoceratium, subgen. nov. . 218 



Macroceratium, subgen. nov. . 218 



Biceratium Vanhoffen . . . 218 



Amphiceratium Vanhoffen . . 219 



Poroceratium Vanhoffen . . . 219 

 The mutation of Ceratium tripos 



to C. californiense .... 220 

 Chronology and nomenclature 



of skeletal parts of chain . . 220 



Genuineness of the chain . . 221 



Completeness of the chain . . 223 



Evidence of mutation .... 224 

 Progressive perfection of the 



mutant ........ 225 



Significance of autotomy and 



resolution of the C. tripos 



skeleton 226 



The mutation between Ceratium 



californiense and C. ostenfeldi 227 

 Evidences of genuineness and 



completeness 228 



Earlier observations on mutations 



in Protista 229 



Mutations in Diatoms .... 229 



Mutations in Destnids .... 232 



Mutations in Ciliates .... 232 



Mutations in Ceratium . . . 233 



Significance of the phenomenon . 235 



Unknown factors 236 



Seasonal polymorphism (Gran 



and Lohmann) 237 



Gamete hypothesis 244 



Degeneration or atavism hy- 

 pothesis 245 



Mutation hypothesis .... 247 



Bibliography 253 



Explanation of Plates 



Normal Schizogony in Ceratium. 



Throughout the genus Ceratium asexual reproduction occurs, in so 

 far as is known, exclusively by schizogony. Multiple spore formation 

 such as is seen in some other genera of diuoflagellates, as for example 



