CHAPTER V 

 METABOLISM OF ANIMALS 



The most important discoveries of the laws, methods, and 

 progress of Nature have nearly always sprung from the exami- 

 nation of the smallest objects which she contains, and from 

 apparently the most insignificant enquiries. Lamarck. 



THERE is probably no better introduction to the study 

 of the biology of an animal than that afforded by PARA- 

 MECIUM, a common organism of ponds, ditches, and decaying 

 vegetable infusions. Paramecium is a representative of 

 some 10,000 kinds of single-celled animals, or PROTOZOA. 

 Members of this group are found in almost every niche in 

 nature and, like the PROTOPHYTA, as the unicellular plants 

 are sometimes called, are important because in numbers there 

 is strength. 



A. STRUCTURE AND LIFE HISTORY OF PARAMECIUM 



Paramecium is a giant among the Protozoa, though just 

 visible to the naked eye as a whitish speck if the water in 

 which it is swimming is properly illuminated. But to make 

 out the details of structure it is necessary to magnify it 

 several hundred times. This done, it appears as a more or 

 less cigar-shaped organism which one would not consider, 

 at first glance, a single cell because it shows highly differen- 

 tiated parts. However, careful study reveals the fact that the 

 organism really consists of a single protoplasmic unit differ- 

 entiated into cytoplasm and nucleus, though each of these 

 regions shows specializations. The nuclear material, instead 



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