kofoid: mutations in ceratium. 247 



represent the first steps in a process whose last stages, judging from 

 conditions in other organisms, would unquestionably be called degenera- 

 tion. There is also a probability that the short-horned heteromorphs ap- 

 proach the ancestral type in form, for the species of the subgenus Bicera- 

 tium are unquestionably more like the other genera of the Peridinidae, 

 for example, like Peridiuium and Gouyaulax, than are the long-horned 

 species of Macroceratium and Tripoceratium. Ceratium minus or C. cali- 

 forniense affords a plausible starting point for the derivation of the other 

 species of the genus, and their occurrence in heteromorphic chains might 

 well be regarded as an atavistic reversion. 



2. Another reason for suggesting that the production of heteromorphs 

 is a degeneration phenomenon lies in the peculiarly hyaline character of 

 the skeleton of C. californiense. It resembles in this respect to some 

 extent the wall of what are probably the cysts of dinoflagellates for which 

 Pouchet (1894) established the genus Sphaerosperma. There are other 

 species in the genus, notably C. teres and possibly C. inclinatum and C. 

 tenuissimum, all of which are relatively small forms, and have to some 

 degree this peculiar hyaline aspect. Sutures are still present in these 

 species, but are often exceedingly difficult to detect. Cysts of dinoflagel- 

 lates have, in so far as they are known, no sutures and are peculiarly 

 hyaline. I have often noted cyst formation (gelatinous or pellicular) in 

 moribund dinoflagellates, and Kllster (1908) finds it in his degenerating 

 cultures of Gymnodinium. This resemblance to cysts on the part of the 

 heteromorph, C. californiense, may be interpreted as an indication of 

 degenerative phenomena, while its appearance in the other species 

 named raises an interesting question as to their possible origin by a pro- 

 cess like that which gives rise to G. californiense, involving, perhaps, 

 certain other dominant and larger species of Ceratium wliich they more 

 or less resemble. 



Mutation Hypothesis. 



The heteromorphs are mutants, the result of the process of muta- 

 tion occurring in nature. The considerations which suppoi't this view 

 are as follows : — 



1. The change is saltatory. It is accomplished in a single schizogony 

 or generation or at the most in two. It is not a process of the slow ac- 

 cumulation of minute variations or a gradual decline in structural 

 characters. In the suddenness of its appearance and the completeness 

 of the transformation the result in Ceratium is comparable with that 

 obtained by DeVries (1905) in Oenothera, Tower (1906) in Leptinotarsa, 

 and Calkins (1906) in Paramecium. 



