244 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



"VVe conclude, then, from an examination of Lohmann's hypothesis of 

 seasonal forms, that the heteromorphs are not of the character to be 

 expected iu seasonal changes, that the evidence of any genetic connec- 

 tion between them and the C. lineatum and C. ehrenhergi of his figures 

 is inconclusive, and that his tables of seasonal distribution of his seasonal 

 forms probably include other species than the heteromorphs and in part 

 illustrate the changing population due to circulation of the Baltic. 



Gamete Hypothesis. 



As a corollary to the first hypothesis of seasonal variation, Lohmann 

 proposes a second, to wit, that the two forms, f. lata and f. lineata, are 

 stages of C. trqjos which conjugate ; that is, they are gametes. The 

 reduction in size which he believes occurs iu the descendants of the 

 heteromorphs of the chains he regards as an adaptation to greater ease of 

 movement on the part of the gametes facilitating conjugation. He calls 

 attention to the occurrence of these so-called gametes immediately after 

 the culmination of the greatest numbers of C. t7-i]pos haJticum, a period 

 when gametes and sexual reproduction would naturally be expected. 



While not accepting his interpretation that all f. lata and f. lineata 

 in his figures and tables are heteromorphs or their derivatives, I believe 

 that the hypothesis that the heteromorphs themselves and their deriva- 

 tive may be gametes must certainly be held open until the actual process 

 of sexual reproduction in some marine species of Ceratium is known. 

 But certain considerations militate against this hypothesis. 



(1) Lohmann lays emphasis upon the reduction in size which he 

 finds in his seasonal forms. The isolated individuals of C. tripos 

 halticum f. lineata are (fide Lohmann) but one tenth and f. lata but one 

 eighth of the volume of C. tripos halticum. The heteromorphs in his 

 chains (fig. II a and III b) show no such reduction in size. I have 

 given above my reasons for doubting the conclusion that all of the 

 isolated individuals showing this reduction belong in the cycle initiated 

 by heteromorphs. I deem it probable that C. lineaium, C. eugramvmm, 

 and C. ehrenhergi have been included by Lohmann -and are the cause of 

 a part, at least, of the seeming reduction he has found. Decrease iu 

 volume, other things being equal, results in increased specific surface, 

 and is, it seems, an adaptation to higher temperatures and decreased 

 molecular friction in the sea water, and may therefore facilitate loco- 

 motion. My contention is only that Lohmann's evidence is inconclusive 

 that the smaller individuals which exhibit this " reduction " lie in the 



