K0F01D : MUTATIONS IN CEBATITJM. 223 



port can also be detected between the older and newer skeletal parts on 

 the two sides of the line of fission in the anterior pair, I 3 and II 3 , of the 

 chain. 



(5) Finally, the nuclear conditions within the cell body (plate 3) in 

 all four individuals are prophetic of another division. It was not pos- 

 sible in the unsectioned preparation to make out finer cytoplasmic struc- 

 tures within the skeletal wall, but the nuclei have either completely 

 divided (IV 3 ) or nearly so (III 3 ) or are plainly in the process of division 

 (II 3 and I 3 ). The division stages here shown are similar to those 

 which Lauterborn (1895) has found in C. MrundineHa, a fresh-water 

 species, and are in all respects of the normal type. There is an ap- 

 parent progression in the stage of mitosis from the anterior schizont 

 posteriorly. 1 



No structural feature is apparent in the individual cells to which this 

 difference in mitotic activity can be traced. There is, for example, no 

 corresponding series of differences in volume of the cell mass, or in ratio 

 of nucleus and cytoplasm. It is possibly of interest in this connection 

 to note that division has progressed farthest in the posterior cells of the 

 chain, those which in normal locomotion are bathed in water which re- 

 ceives the waste products of the more anteriorly located members of the 

 chain. Locomotion occurs in chains of Ceratium even during division, 

 for the flagella persists during the process of schizogony (see Lauterborn, 

 1895). I have myself seen chains in locomotion with active flagella in 

 recently collected plankton, quite contrary to the observations of Murray 

 and Tizard (1882). 



Completeness of the Chain. 



Not only is this a genuine chain, but it is in all probability a complete 

 chain. The presence of a long anterior horn with squarely truncate tip 

 upon the foremost cell of the chain is conclusive evidence that the chain 

 is complete in that region, that is, that no schizonts have cut loose from 

 the chain at this end during the present cycle of schizogony. The tip of 

 all young apical horns is peculiarly asymmetrical in adaptation to chain 



1 In view of the many discussions over the direction of the plane of division 

 among flagellates, especially in parasitic forms such as Spirochaeta and Trypa- 

 nosoma, it is of interest to note here that during the process of mitosis the 

 equatorial plane or cleft between the parting chromatin masses shifts from approx- 

 imately a longitudinal position to one at 45° to the major axis. The seemingly 

 oblique division of the dinoflagellates is thus in its relation to the position of the 

 nucleus prior to mitosis, a longitudinal one. It is, however, oblique in the skeleton 

 and also in the plasma, unless the latter shifts with the nucleus. 



