KOFOID: MUTATIONS IN CERATIUM. 251 



certain instances of heteromorphic chains is perhaps indicative of adverse 

 conditions, such as sinking to a zone of low temperature. The return of 

 such an individual to the upper levels by the vertical movement of the 

 water might afford the occasion for renewed growth and reproduction for 

 cells in suitable physiological stages. The schizogony which ensues re- 

 sults at once in a mutation, and with the new generation the line of 

 descent passes into a new or different stage of equilibrium. 



These heteromorphic changes in Ceratium occur in the course of asex- 

 ual reproduction. There is no evidence that the parent cell is a zygote 

 or one of a recently conjugated pair of gametes. If the idea of the indi- 

 vidual is conceived in the Huxleyan sense, these mutants and those of 

 the diatoms belong in the same category as bud sports and are to be re- 

 garded as isolated apical cells which have abruptly assumed new or 

 different specific characters. Will the next sexual reproduction in the 

 line of descent be followed by a I'eversiou to the old form ? Certain 

 studies on bud sports (see MacDongal, Vail, Shull, 1907) indicate the 

 permanence of the change. 



The occurrence of mutations in the asexually reproduced individuals 

 of Ceratium bring additional confirmation to the idea that mutations are 

 not necessarily dependent upon sexual reproduction for their appearance, 

 bnt are a manifestation of a fundamental property of protoplasm of plants 

 and animals alike, a property which is variously manifested in the muta- 

 tions of sexually produced organisms, as in the elementary species of 

 Oenothera, in the results of the hybridization including those which 

 follow the Mendelian formulae, in those in wdiich asexual reproduction 

 occurs, as in bud sports and in these heteromorphs of Ceratium, and 

 perhaps, also, in many types of neoplasms afld abnormalities. They are 

 a manifestation of unit systems (see Eitter, 1907) changing under 

 stimulus in kaleidoscopic fashion from one stage of equilibrium to 

 another. 



Tlie seeming reversion in these mutants of Ceratium to old and funda- 

 mental subgeneric types, the occasional reversibility of mutations else- 

 where, and the limitations in the range and number of mutant types 

 appearing generally in nature and under culture, suggest that the chemi- 

 cal nature of living substances and the ever fleeting organization of these 

 substances in equilibriums of living structures which we call organisms, 

 place certain rather definite restrictions upon the number and amplitude 

 of the departures which mutants make from their sources. From the 

 point of view of mutation the relation which exists among the members 

 of a group of elementary species, or perhaps among the species of a 



