kofoid: mutations in cekatium. 



221 



patent that each individual possesses one moiety of the latest generation, 

 while the other has descended from some antecedent one. 



Ii 



An inspection of the figures on plates 1-3 and a comparison of the 

 skeletal conditions there presented makes it evident that the present 

 chain reveals, by virtue of the existence of fixed skeletal parts passed 

 by " down inheritance," the skeletal morphology for three generations. 

 The chains of Ceratium offer thus a unique opportunity for the study of 

 pedigree cultures in relatively simple organisms. The species characters 

 in Ceratium lie mainly in the skeletal parts, and these are so preserved 

 in later generations that the skeletal morphology of a line of descent may 

 be traced with a degree of certainty unsurpassed in other organisms. 

 The genetic connection of the members of the chain is insured beyond all 

 question, a condition difficult to realize where the schizonts are separated 

 at the close of cell division. Furthermore there can be no possibility of 

 accidental contamination of a culture from air-borne spores or encysted 

 forms such as must always attend pedigree culture work with most 

 flagellates and ciliates. 



Genuineness of the Chain. 



This is, beyond all question, a genuine chain of genetically related 

 Ceratium formed by schizogony with skeletal and plasmatic continuity, 

 as is usual in chain formation. It is not a chance assemblage of indi- 

 viduals, jostled together in the crowded collection. Neither is the pos- 

 terior member of the series accidentally attached to a chain of unrelated 

 origin. The following facts sustain this assertion : — 



