PHYSIOLOGY OF THE CELL. 



45 



it lies near the nucleus, surrounded by a clear zone, from which 

 delicate threads radiate through an area known as the attraction 

 sphere. The nucleus enlarges and becomes richer in chromatin. 

 The lateral twigs of the chromatin cords are drawn in, while 

 the main cords become much contorted. These cords 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 field, while 

 the other ends interdigitate on the opposite side of the nucleus 



Close Skein 

 (viewed from 

 the side). 

 Polar field. 



Loose Skein (viewed 

 from above i. e., from 



the pole). Mother Stars (viewed from the side). 



Spindle. 



Mother Star (viewed Daughter Star, 

 from above). 



Beginning Completed 



Division of the Protoplasm. 



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

 CAVITY or 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 mag- 

 nification. X 560. 



the anti-pole. The polar field corresponds to the area occu- 

 pied by the centrosoma. This arrangement is known as the 

 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 centrosoma divides into two portions, 

 which move apart to positions at the opposite ends of the long 

 axis of the nucleus. At the same time delicate achromatin 

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



