2 Froceeding^ of the Royal Irish Academy. 



Tlie stages of the process of mitosis in the spore-mother-cells, 

 acknowledged by all observers, may be briefly summarized as 

 follows : — 



(1.) The " dolichonema " stage, fig. 1. — The large nucleus of the 

 spore-mother-cells is occupied by an enormously long and attenuate 

 thread, consisting of a single series of chromatin granules (the chro- 

 momeres) imbedded in the linin matrix. This thread presents few or 

 no anastomoses. 



(2.) In the next stage (fig. 2) the nucleus is in what I would 

 suggest to call the " strepsinema " condition. The chromatin appears 

 in much the same condition as in the preceding stage, except that in 

 many places it may be seen that two portions of the thread are more 

 or less loosely twisted together. The later this stage is observed, the 

 thicker the chromatin thread appears, and the greater the amount of 

 the thread so twisted. 



(3.) The thick twisted chromatin thread appears broken into a 

 number of chromosomes, which have the form of twisted loops 

 or two short threads twisted together, with four free ends, or of rings 

 (figs. 3 and 4). The number of these chromosomes is half that found 

 in the nuclei of vegetative cells. In the later periods of this stage the 

 chromosomes are thicker than at the beginning, and the separate 

 chromomeres in the threads are no longer visible. 



During these first three stages the nuclear membrane remains 

 intact, and one or more nucleoli of large but gradually waning dimen- 

 sions are present in the nuclear fluid. 



(4.) Nuclear plate (figs. 5 and 6). — The thickened chromosomes, 

 composed of two portions twisted together, lie radially disposed in the 

 equatorial plane of the nucleus, and attached by their internal 

 extremities to the fibres of the achromatic spindle. The nuclear 

 membrane and large nucleoli have disappeared. 



(5.) Metaphase (fig. 7).— Two thin V-shaped daughter chromo- 

 somes occupy the place of each of the thick twisted chromosomes 

 in the equatorial plane. They are so disposed that the apices of 

 the Vs point towards the poles of nucleus, while the two free ends 

 of one are in contact with the ends of its fellow in the equatorial 

 plane. 



(6.) Anaphase (fig. 8). — The daughter chromosomes lie round the 

 poles ; they are still V-shaped, but the limbs of each V have become 



