UNICELLULAR FORMS 



69 



is employed to describe this specialization of structure and meta- 

 bolic activity. 





>»>■ 



12 3 



Fig. 19. — The "trial and error" method of solving difficulties as illustrated by the 

 attempts of a paramaecium to pass by an obstacle. (After Jennings: Behavior of the 

 Lower Organisms. Columbia University Press.) 



Reproduction in Paramoecium. Paramcecium reproduces 

 by binary fission (Fig. 20). Preceding division, the oral groove dis- 

 appears. Both the macronucleus and the micronucleus elongate 



DIVISION PLANE— ^ 



MACRONUCLEUS 



MICRONUCLEUS 



Fig. 20. — Binary fission of a paramoecium. 



and at the same time a constriction appears about the animal. Di- 

 vision is completed when the elongated nuclei have separated into 

 two and the constriction has progressed to separate the parent ani- 



