FACTORS IN ONTOGENY 



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FIG. 145. Cell fission in the salamander: A, Resting nucleus stage, centrosome partly 

 developed; B, skein stage, chromatin visible as a convoluted hand, the centrosomes 

 having separated; C, the nuclear membrane having disappeared, and a few of the 

 chromosomes lying free in the cytoplasm; D, central spindle complete, the chro- 

 mosomes on splitting being drawn to the spindle; E, metaphase; F, anaphase, the 

 chromosomes being drawn to the poles. (After Driiner.) 



