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Nov.. 19210 CYTOLOGICAL STUDIES ON P0BPH7RA TENERA, 209 



clironiatic portion covering the achromatic core splits into three 

 filaments by longitudinal fissures as represented in Fig. 2, d, k ; 

 the polar view of the filaments in this stage is shown in Fig. 3. 

 The fissures just mentioned generally do not go further, so that the 

 filaments are not completly separated from each other at both ends, 

 where unseparated portion generally passes into a fine process. And 

 the substance constituting the achromatic core of the nncleus becomes 

 mixed with the surrounding cytoplasm through the fissures. 



Then the middle part of each filament gradually becomes thinner 

 and finally it breaks up into two segments. These daughter segments 

 go to opposite poles ; and the three daughter segments thus formed 

 draw together in each pole where a new nucleus is formed. Details of 

 this process are drawn in Fig. 2, a— h. Gardner (3) has figured suc- 

 ceeding stages of the dividing nucleus of Synecocystis aquatilis in the 

 paper on Cyanophycese ; it is interesting to notice that his Figs. 41 

 and 42 closely resemble Fig. 2, d, e of mine. A further discussion on 

 this point is deferred to a later page. 



Judging from the process of the nuclear division just mentioned, 

 the chromatic filament which seems to convey the essential part of 

 the dividing nucleus may be regarded as the chromosome of a primi- 

 tive type. The presence of a definite number of the chromatic fila- 

 ments in every case of the nuclear division and their migration to 

 the definite poles may be taken as the characteristic of the mitosis, 

 wheras such a simple feature as the transverse breaking of the fila- 

 ments reminds one of amitosis. From these phenomena the mode of 

 the nuclear division of Porphyra tenera may be taken as a primitive 

 mitois. It is often met with in the dividing nucleus that the chro- 

 matic portion is divided into two cup-shaped halves, each of which 

 is provided with tripodial processes, or two chromatic filaments are 

 seen nnited to a single thicker thread (Fig. 2, 1). 



The two daughter nuclei take the opposite course, making their 

 way toward the adjoining wall of cell. Then the division of pyrenoid 

 takes place by a constriction which is followed by the division of 

 chromatophore in the same way ; the dividing plane is always 

 parallel to the lateral that is the adjoing walls, toward which the 

 daughter nuclei have moved. The cross wall is now laid down, 

 which is ring-shaped at first, and gradually grows toward the centre 

 of the ring. The upper one of the cells shown in Fig. 5 illustrates 

 a stage of cell division. It is a dividing antheridial cell, but the 

 essential mode of division is quite same as in the vegetative cell. 



