1907] APOGAMV IN NEPHRODIUM 143 



The cliromosomes at the equatorial plate split longitudinally, 

 and, after a peculiar change of their fornij two groups of daughter 

 chromosomes pass to the opposite poles of the spindle^ where they 

 become closely crowded in a mass. The polar view of this stage 

 shows that the number of chromosomes is 128 or 132. Nucleoli 

 fuse usually into one or two globules which decrease in size, finally 

 vanishing during the prophase. The daughter chromosomes, 

 crowded in a mass at the poles of the spindle, become so closely 

 aggregated that it is hard to identify their individual outlines; then 

 follows vacuolization of each chromosome. 



The central spindle lying between two poles, after organization 

 of the daughter nuclei seems to contribute material for the formation 

 of the cell plate, and consequently it proceeds from the center toward 

 the periphery of the cell. 



The resting nucleus of the spore mother cell contains a fine net- 

 work of linin, in w^hich the chromatin material is distributed in larger 

 and smaller knots. With the further growth of the nucleus, the knots 

 in the netw^ork decrease in size, whereas the delicate linin part increases 

 in thickness, and finally there is formed a well-developed spirem, uni- 

 form in thickness and very much tangled. This state soon passes 

 into the synaptic stage, which seems to culminate by location of the 

 tangled spirem at one side of the nuclear cavity. The spirem consists 

 of two threads, close together; in some parts the two are in contact 

 side by side, and in the other parts they arc fused into a single thread. 

 These two threads may represent, according to the recent interpreta- 

 tion of synapsis, chromatin of maternal and paternal origin. 



After synapsis, the tangled thread begins to uncoil and becomes 

 distributed throughout the nuclear cavity; the spirem shows longi- 

 tudinal splitting, but the two elements of the spirem which resulted 

 therefrom remain closely associated so as to form a double thread, 

 which finally segments into 66 or 64 chromosomes, each showing 

 clearly its bivalent nature. 



Fibrillar structures which first appear at the periphery of the clear 

 region closely surrounding the nucleus become more and more 

 pronounced until they approach the nuclear membrane, and when 

 the membrane breaks down the fibers enter into the nuclear cavity from " 



several directions. 



