PROTOZOA. 



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lar cells, we find something of the variety of shape which we 

 observed in the tissue cells of the higher animals (Chapter V). 

 The Protozoa are especially interesting to the biologist because 

 they represent the simplest forms of animal life now found 

 on the earth and because some of their representatives are very 

 like some of the simplest plants. Indeed some of them are 

 claimed by both the botanists and the zoologists. It also seems 

 probable that the first animal life to appear on the globe had 

 the general characteristics of some of the Protozoa. Whether 

 some type of protozoan is to be considered as the ancestor of 

 the higher many-celled animals or not, it is true that we find 

 illustrated here in the simplest possible way the beginning of 

 all those functions which are so completely distributed among 

 the special organs of the complex animals. The Paramecium 

 does in a simple yet satisfactory way all that any living animal 

 needs to do in order to live and perpetuate its species. 



FIG. 65. 



FIG. 65. Amoeba, ec., ectosarc; en., endosarc, containing food vacuoles (f) ; n, 

 nucleus; p, pseudopodium; p.v., pulsating vacuole. 



Questions on the figure. Define the various terms used above in 

 describing the parts of the amoeba. What changes may the amoeba undergo 

 in its life history? Compare figures i and 6. 



1 88. General Characters. 



1. Mostly unicellular throughout life. May have one or 

 more nuclei (Figs. 66-69). 



2. The protoplasm usually consists of a clearer outer por- 

 tion (ectosarc} and a more granular inside portion (endosarc) 

 (Fig. 66, ec, en). 



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