2l6 



REPRODUCTION 



double pieces, or pairs of chromosomes (Fig. 123, B, c and d). 

 These become thicker and dispose themselves at the equator 

 of the nucleus; the nuclear membrane disappears and proto- 

 plasmic threads radiating from the poles of the cell fasten upon 

 the members of the pairs of chromosomes in such a way as to 

 draw them apart toward opposite poles, twenty-two chromo- 

 somes to each pole (Fig. 123, C, e and/). As they move toward 

 the poles it is seen that they have become divided longitudinally 



B 



Fig. 123. — Formation and separation of chromosomes in the spore grandmother cells 

 of Osmunda cinnamomea. .4 , a, early prophase showing approx iniation of nuclear thread 

 in parallel strands; b, detail more highly magnified; B, later prophase showing transverse 

 division of double thread, forming pairs of chromosomes; d, two pairs of chromosomes 

 from c more highly magnified; C, e, metaphase showing separation of the members of the 

 chromosome pairs;/, late anaphase showing that each chromosome is longitudinally split. 

 Further description in the text. (After Yamanouchi.) 



through the middle (Fig. 123, C, /), and that the halves spread 

 apart at their equatorial ends while remaining together at their 

 polar ends. 



At the poles these longitudinally-split chromosomes branch 

 out more or less into a reticulum and a nuclear membrane is 

 formed; but soon the second division is begun, the split chromo- 

 somes become again recognizable, and give evidence by this 

 fact that they had preserved their identity through the resting 

 period. The nuclear membrane now disappears, the chromo- 

 somes become lined up at the equator, and strands of cytoplasm 

 pressing in from opposite poles become attached to the longit- 

 udinal halves and draw them one to one pole and one to the 



