PELAGIC PLANT LIFE 



325 



adaptations from one generation to the othier. Still, now and 

 then even this, too, is possible. I found during the Atlantic 

 expedition of the " Michael Sars " that the subtropical Ceratium 

 platycorne, both of the posterior horns of which are developed 

 ordinarily into flat wing-like suspension-organs, changed gradu- 

 ally into a form with cylindrical horns belonging to the Gulf 

 Stream in the Norwegian Sea, that I 

 had myself previously described under 

 the name of Ceratium compresstnn (see 

 Fig. 228). 



Discontinuous variations have been 

 found as well as continuous ones in the 

 species of Ceratitim. Lohmann has Lohmann. 

 shown that the ordinary Baltic form, 

 C. tripos, can set up an intermediate 

 generation of a totally different type, 

 much smaller and with short, straight 

 horns, corresponding to the forms de- 

 scribed under the name of C. lineatttm. 

 Kofoid has met with similar variations 

 in American species (see Fig. 229). The 

 signification of these development forms 

 has not yet been discovered. Jorgen- jcirgensen. 

 sen, who has recently published a mono- 

 graph on the genus, is inclined to 

 regard them as degenerate forms that 

 have been produced under abnormal 

 conditions of existence. It seems to 

 me, however, more probable that these 



Only one cell IV. I shows the charac- , , i -i n 1 



ter of the type, the others (I. -III.) Small, extrcmely mobile, cells are normal 

 belonging to the type of pm//««/ formations, which have a definite func- 



cali forii tense {^\"). (Kotoid. ) . - . , . _ , - 



tion to perform m the imperfectly known 

 development - cycle of the species of Ceratium. It is still 

 questionable whether peridinese propagate sexually, even though 

 Zederbauer claims to have discovered sexual propagation in the Zederbauer. 

 ordinary fresh-water form [Cei^atium hirundinella\ But, a 

 priori, it is quite possible that the above described inter- 

 mediate generation may be a sex-generation. Just as little as 

 these "mutations" do we understand the significance of the 

 gemmation which Apstein has lately described in Ceratium Apstein. 

 tripos, nor do we know what conditions of existence cause 

 gemmation instead of normal cell-division. 



Another important genus with many species, Peridirmtm, Peridinium. 



Fig. 229. 

 Ch.vin of Ceratium tripos. 



