236 bulletin: museum of comparative zoology. 



clearness the transmutation in' form while the accessory phenomenon of 

 chain formation renders possible a rigorous certainty in determining the 

 line of descent. These changes give rise, not to new types, hitherto 

 unknown, but old well-known types give rise suddenly to others old 

 and well known or at least previously known. The particular category 

 to which these types are referred, species, subspecies, varieties, or forms, 

 is a subordinate matter. For convenience in discussion and also as an 

 expression of my own opinion I have regarded them iu the preceding 

 pages as species and shall continue to do so in those that follow. The 

 importance of the change in form is, however, not removed by a change 

 in the category to which they are assigned. The fact here remains that 

 like gives rise to unlike, that the descendents differ profoundly from the 

 ancestral type. 



Unknown Factors. 



What, then, is the biological significance of these abrupt changes ? No 

 conclusive answer at present can be given to the question, for there are 

 so many deficiencies in our knowledge of dinoflagellates in general, of the 

 conditions of life in the sea, and of the prevalent causes and consequences 

 of these phenomena of sudden change, that all conclusions must contain 

 a large element of uncertainty owing to this relatively narrow basis of fact. 

 For example, we know as yet nothing of sexual reproduction in the marine 

 dinoflagellates beyond the occurrence of resting spores that possibly have 

 a sexual origin. Are special gametes formed, or are all schizonts capable 

 of conjugation 1 We have as yet no adequate quantitative studies of the 

 extent and character of variation in the species of the genus nor correla- 

 tion of these changes with the physical factors of the environment such 

 as the temperature, salinity, and molecular friction. Ostwald's (1903) 

 theoretical formulas regarding specific surface and molecular friction are 

 yet to be put to the test of a practical application in Ceratium. Are 

 species with different specific surfaces and individuals within the species 

 having different surfaces distributed in the sea at such seasons and in 

 such places as to conform to Ostwald's computations'? Will Entz's 

 (1905) conjectures as to the existence of universal intergradations of 

 species in the genus Ceratium bear the test of an intensive study by the 

 statistical method? Will Lohmann's (1908) suggestion of a widespread 

 seasonal polymorphism in the genus find confirmation in pedigree 

 cultures 1 



Beyond the instances here recorded we know nothing of the extent to 

 which these changes occur in nature, nothing of their seasonal and geo- 



