240 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



(temperature) variations leave the general facies or habitus of the or- 

 ganism unchanged, and are not of the abrupt type seen in these hetero- 

 morphic chains where the whole form of the organism is suddenly recast 

 in another entirely distinct mould or pattern. These seasonal changes 

 belong rather to the fluctuating type of variations, while those of the 

 heteromorphic chains are saltatory in character. 



The physical conditions prevalent at the time of the greatest increase 

 (September 7-28) in numbers of these smaller individuals (see Lohmann's 

 table, p. 242-243) give a constant index of molecular friction (64.5 to 65). 

 It is also a period of falling temperatures. Lohmann's conclusions and 

 tables require that in the face of this C. tripos balticum should give rise 

 (on September 28) to 53.5 short-horned individuals to 100 of the type, 

 individuals moreover of much smaller size and therefore of greatly in- 

 creased specific surface. The volumes of G. tripos balticum, its f. lineata 

 and f. lata are given in Tabelle B (Lohmann) as 100,000, 8,000, and 

 10,000 cubic micromillimeters respectively. (The volumes of the two 

 forms are stated on p. 271 to be 1/8 and 1/10, respectively, of that of 

 the type.) This means at least a doubling of the specific surface of the 

 organism in the " seasonal change." With constant molecular friction 

 and falling temperature it seems incredible that Ceratium tripos should 

 suddenly give rise to considerable numbers of smaller forms, " seasonal 

 variations," in which the specific surface of the organism is doubled, an 

 adaptation to rising temperature and falling molecular friction ! This is 

 an additional reason for believing that these smaller forms do not lie in 

 the genetic cycle of O. tripos balticum, but are independent species 

 included incorrectly in Lohmann's tables, and that their sudden increase 

 in the plankton of Kiel was due to other causes than seasonal variation 

 of C. tripos. 



(2) The known distribution of Ceratium lineatum (sensu latu), C. cali- 

 forniense, and G. minus affords no satisfactory basis for regarding them 

 elsewhere as seasonal forms of C. tripos. . The former species (sensu latu) 

 (Cleve, 1900, 1902) has a wide range of distribution in colder and 

 warmer seas, as has also G. tripjos (sensu, latu). In the seasonal and 

 geographical distribution of C. lineatum (sensu latu) and C. minus and 

 forms resembling it in the Pacific Ocean, I have found no indications 

 which suggest that the two form a part of the genetic cycle of Ceratium 

 tripos with seasonal limitations. 



(3) The numerical proportions of Ceratium tripos balticum and the 

 f. hneata (Ehrbg.) Lohmann and lata Lohmann are hardly those that 

 would be expected if the latter are seasonal forms of the first. We would 



