O THE CELL 



when seen from the side, they make a star, called the mother 

 star or aster. While the loose skeins are forming, delicate 

 striae appear within the achromatin, so disposed as to make 

 their bases within the polar field and directed toward one 

 another, and their apices directed toward the future new nu- 

 clei. These achromatin figures constitute the nuclear 

 spindle. They then arrange themselves into two daughter 

 wreaths, or asters, similar to the mother star. At this junc- 

 ture the cell protoplasm begins to divide by becoming con- 

 stricted in the center. The daughter stars are converted into 

 two new nuclei, in the inverse order to that by which the 

 original nucleus was broken up. Nuclear membranes and 

 nucleoli appear, the cell protoplasm divides into two new 

 cells, and the cycle is completed. 



Derivation of Tissues. The primary parent cell divides 

 into an innumerable mass of cells which is called the blasto- 

 derm. The blastoderm soon divides into two more or less 

 distinct layers, an outer and an inner, named ectoderm and 

 entoderm, between which a middle layer develops, the meso- 

 derm. From these three primary layers all of the various 

 tissues of the body are later developed. (See Embryology.) 



