kofoid: mutations in ceratium. 235 



The second chain figured by Lohmann (lig. E) consists also of two 

 individuals. The rear cell is designated by him as C. tripos balticum 

 forma truncata, and the forward cell as C. tripos balticum forma lineata. 

 As I have elsewhere (Kofoid, 1908) shown, autotomy is of wide occur- 

 rence in the genus Ceratium. It is a degeneration phenomenon taking 

 place in advei'se conditions which, in plankton sinking to deeper and 

 colder waters, is correlated with flotation and assumes an adaptive sig- 

 nificance. The posterior member is an autotomized individual of C. tripos 

 balticum. The anterior member resembles the species described by 

 Ehrenberg from the northern waters as C. lineatum and appearing often 

 in the literature of recent years as C. furca balticum Moebius, a spurious 

 name, for Moebius never described such a species. 



Lohmann's forma lineata as seen in the anterior cell (heteromorph) 

 of his figure III b has certain structural features in which it resembles 

 his f. lata ; such as the form and pi-opoi'tions of the midbody, the shape 

 of the ventral plate, the divergence of the right horn, and the dimensions 

 of the cell. It differs in its tapering posteriorly directed left antapical 

 horn. This difference may be partially accounted for by the seeming 

 obliquity of the view shown in Lohmann's figure III b. In it the left 

 side of both cells is relatively expanded and the right foreshortened, and 

 the left horn may be so placed that any divergence is obscured by the 

 angle of vision. A close relationship between the heteromorphs of the 

 two chains figured by Lohmann is, in the light of these considerations, 

 not improbable. 



Tlie cells of this chain are representatives of the two subgenera Tripo- 

 ceratium and Biceratium. By reason of the considerable length of the 

 apical horn of the anterior schizont and the autotomy of the antapicals 

 of the posterior one, the chain may be regarded as complete or entire, the 

 result of a single schizogony, in which occurs a complete saltation from 

 C. tripos balticum to a form resembling C. lineatum, with less apparent 

 tendency to produce an intermediate condition such as is manifested 

 in the other chain Lohmann figures (fig. D) or in that shown in 

 plates 1-3. 



Significance of the Phenomenon. 



The fact of supreme importance in the phenomena recorded by Loh- 

 mann (1908) and observed by myself in greater diversity, is the abrupt 

 and complete change in form in a line of descent in a single, or at the 

 most in two generations of organisms asexually reproduced. The change 

 is recorded in immovable skeletal parts which reveal with unmistakable 



