HUMAN PHYSIOLOGY. 



have a general direction transverse to the long axis of the cell, and parallel 

 to the plane of future cleavage. They are seen as V-shaped segments or 

 loops, chromosomes, having their closed ends directed toward a common 

 center, the polar fold, while the other ends interdigitate on the opposite 

 side of the nucleus the anti-pole. The polar field corresponds to the 

 area occupied by the centrosome. This arrangement is known as the 



Cbse Skein 

 (viewed from 



the side). 

 Polar field. 



Loose Skein (viewed 

 from above i. e., from 

 the pole). 



Mother Stars (viewed from the side) . 



Mother Star (viewed Daughter Star. Beginning. Completed. 



from above). Division of the Protoplasm. 3 



FIG. 3. KARYOKINETIC FIGURES OBSERVED IN THE EPITHELIUM OP THE ORAL 



CAVITY OF A SALAMANDER. 



The picture in the upper right-hand corner is from a section through a dividing 

 egg of Siredon pisciformis. Neither the centrosomes nor the first stages of the 

 development of the spindle can be seen by this magnification. X 560. 



close skein; but as the process goes on, the chromosomes become thicker, 

 shorter and less contorted, producing a much looser arrangement, known 

 as the loose skein. During the formation of the loose skein, the centro- 

 some divides into two portions, which move apart to positions at the oppo- 

 site ends of the long axis of the nucleus. At the same time delicate achro- 

 matin fibers make their appearance, arranged in the form of a double cone, 

 the apices of which correspond in position to the centrosome. This is 

 known as the nuclear spindle. During the prophase the nuclear mem- 

 brane and the nucleoli disappear. 



