kofoid: mutations in ceratium. 245 



same genetic cycle with the larger C. tripos and are therefore to be 

 regarded as gametes of that species. 



(2) Both C. tripos and C. ostenfeldi (plate 1 and plate 4, fig. 4) 

 have been found by me in chain with the same type of heteromorph. 

 There is, as I have shown (p. 228), some difficulty in determining what 

 the ancestral cell was in the heteromorphic chain containing C. osten- 

 feldi and C. californiense. In any event it seems improbable that we 

 should find the same type of skeleton-bearing gamete for the two species 

 C. tripos and C. ostenfeldi, or that C. mliforniense, being a gamete of 

 C. tripos, should give rise to C. ostenfeldi by schizogony. Any inter- 

 pretation of this chain in accord with the gamete tlieory is, with our 

 present knowledge, beset with difficulties. 



(3) The known cases of conjugation in Ceratium do not lend support 

 to the view that special gametes mai'ked by a sudden change in form 

 from the parent type are produced prior to conjugation. Zederbauer's 

 (1904) and Entz's (1907) description of conjugation in C. hirundinella, 

 a fresh water species, shows the union of normal forms of that species. 

 Pouchet (1885) figures two cases of the union of two individuals of 

 C. fusus in ventral apposition with extruded (]) plasma in one case, and 

 another instance of conjugation (1) of C. biceps has come under my observa- 

 tion. In all three instances presumably of conjugation, the gametes are 

 normal individuals of the species. 



If these heteromorphs are neither seasonal forms nor gametes, what 

 is their biological significance ] I have two alternative hypotheses to 

 make, both provisional in view of our imperfect knowledge of the pro- 

 cess and its results with which we are dealing, hypotheses, moreover, 

 which are perhaps not mutually exclusive but merely two aspects of, 

 or methods of approach to, a common phenomenon. 



Degeneration or Atavism Hypothesis. 

 The heteromorphs are degenerate or atavistic forms of dominant 

 thriving species called forth by the impact of new and perhaps adverse 

 conditions to which they are subjected by the circulation of the sea or 

 their own active or passive movements principally in the vertical direc- 

 tion. The exceedingly great sensitiveness of pelagic organisms to even 

 slight changes in their environment is quickly impressed upon one who 

 works with living plankton or traces their vertical and horizontal dis- 

 tribution. For example, certain species of dinoflagellates rarely appear 

 in the plankton taken near shore at San Diego or Naples, but only at a 

 distance of several kilometers. A similar phenomenon appears also in the 



