CELL DIVISION 



49 



the chromosomes, which are believed to be the bearers of the 

 hereditary qualities which can be handed down from parent to 

 offspring. 



cell tfrows equatorial - 



and ctiviotes pi cxne^ 4. 



_ chromosomes; 



ST Splits anot _ 



travel to*&ret 



ypoles 



An animal cell showing mitotic division. During this division the chromatin granules form 

 a coiled thread which finally breaks up into chromosomes. Each chromosome splits into two 

 similar parts which go to the opposite ends of the cell, where they become a part of two 

 new nuclei. At the same time a small structure, the centrosome, separates into two parts. A 

 wall forms midway between the two nuclei, and the cell divides, forming two cells. 



Self-Testing Exercise 



Cells are the units of (1) of plants and animals. A plant 



cell differs from an animal cell by having a (2) (3) and 



containing (4). All cells contain a (5). Cells grow 



by (6) . Hereditary qualities are handed down from one 



generation to another by means of the (7) in the (8) 



(9). A collection of like cells is called a (10). 



An organ is made up of a (11) of (12) acting to- 

 gether to do (13). 



PROBLEM IV. WHAT DO WE MEAN BY ADAPTATION? 



Demonstration 6. Show by means of charts, pictures, and actual 

 examples, a number of adaptations such as bills and legs of birds ; wings 

 of insects; teeth of carnivorous animals. Protective coloring in in- 

 sects, and adaptations in plants, especially in cactus, pitcher plant, 



