VARIATION IN UNICELLULAR ORGANISMS 



97 



When we examine unicellular organisms, we find that the 

 individuals of a species differ among themselves, just as is 

 true in higher organisms. If one collects a large number of 

 individuals of some unicellular animal — say Paramecium, or 



B 



Figure 75. Reproduction and development in the infusorian Stylony- 

 chia, after Wallengren, 1901. A. Parent before division, showing the 

 number and distribution of the locomotor appendages. B. Beginning 

 of division: appearance of two groups of small projections, that are 

 later to form by enlargement and distribution the appendages of the 

 two offspring. C. Later stage of division: the two groups of embryonic 

 appendages are scattering to take their final positions. The old 

 appendages have not yet disappeared. 



Difflugia, or Arcella — one usually finds diversities of many 

 kinds among them. In the shelled rhizopod Difflugia corona 

 (Figure 16), an animal closely related to Amoeba, one finds 

 the individuals differing greatly in size, form and structure of 

 their shells, as well as in many physiological ways. Many 



