296 Phillips on a Comparative Study of the 



a multiplication of the number of granules upon the net. 

 Thereafter two modes of division may occur, even in the 

 same species. In the first method (Figs, i to 5, 16 to 20), 

 the central body or nucleus does not get beyond the network 

 stage. This network draws together along the equator 

 of the cell (Fig. 3), the net becoming finer and denser. 

 It then begins to constrict in the middle (Figs. 4, 7). The 

 side walls grow inward, first as a delicate collar of micro- 

 somata, gradually becoming stronger and deeper, until 

 finally the network is constricted entirely, and the micro- 

 somata harden into a division wall. In this mode of divi- 

 sion, the nucleus becomes constricted in dumb-bell fashion. 

 The halves are usually as nearly equal as can be determined 

 by the microscope, but at times one will appear considerably 

 larger than the other. Lauterborn (47b) has noted that the 

 nucleus of Dinoflagellates divided in the spireme stage, 

 though there the divisions and the spiremes were more 

 typically mitotic than in the Cyanophycese. 



The other method of division is undoubtedly a primitive 

 mode of karyokinesis. The network is the same as has 

 just been described for the first method of division, but 

 instead of constricting itself into two parts while in the net 

 stage, the chromatin network resolves itself into a single 

 coiled linin thread (Figs. 8, 68), or spireme, upon which the 

 balls of chromatin are arranged one against the other like a 

 string of beads. This spireme arranges itself along the 

 longitudinal axis of the cell, and breaks up into segments of 

 about equal length (Figs. 9, 69). These segments might be 

 termed chromosomes, though they do not form a nuclear 

 plate, but are arranged along the whole of the segment 

 in the form of the original beads of chromatin that were 

 found in the net and spireme. That these beads cannot 

 be termed chromosomes is evidenced by the fact that they 

 usually retain their identity until after the daughter chromo- 

 somes are formed, each daughter chromosome being com- 

 posed of several of them. The segments do not converge to 



