178 



DIVISION OF LABOR 



Physiological Division of Labor. — If we compare the amoeba 

 and the parama?fium, we find the latter a more complex organism 



Stages in the development of a fertilized egg into the gastrula stage. Read your 

 text, then draw these stages and name each stage. 



than the former. An amoeba may take in food through any part 

 of the body ; the paramoecium has a definite gullet ; the amoeba 



may use any part of the 

 body for locomotion; the 

 paramoecium has definite 

 parts of the cell, the cilia, 

 fitted for this work. Since 

 the structure of the para- 

 moecium is more complex, 

 we say that it is a '' higher " 

 animal. In the vorticella, a 

 still more complex cell, part 

 of the cell has grown out 

 like a stalk, has become 

 contractile, and acts like 

 muscle. 



As we look higher in the 

 scale of life, we inva- 



Photo^^ruph of a living vorticella, showing the • ui fl j x, . pprtflin 



contractile stalk and the cilia around th ^ ^laDiy nno tnaL certam 



mouth. Compare this figure with that of the parts of a plant or animal 



paramoecium. Which cell shows greater , i. 4. j 



division of labor ? are Set apart to do cer- 



tain work, and only that 

 work. Just as in a community of people, there are some 

 men who do rough manual work, others who are skilled work- 

 men, some who are shopkeepers, and still others who are profes- 



