54 



ANIMAL BIOLOGY 



are parasitic: there is a highly complex fauna in the digestive 

 tract of horses and cattle, and Man is not immune. (Figs. 18, 26.) 

 The organization of the group may be illustrated by Paramecium 

 which is a giant among the Protozoa, being just visible to the naked 

 eye as a whitish speck if the water in which it is swimming is 



Prorodon 



Euplotes 



Didinium 



Stentor 



Stylonichia 



Lionotus 



i 



Lacrymaria 



Spirostomum 



Fig. 26. — Common ciliated Protozoa (Infusoria) from fresh water. (From 



Curtis and Guthrie.) 



properly illuminated. When magnified several hundred times it 

 appears as a more or less slipper-shaped organism which one would 

 not consider, at first glance, a single cell because it shows highly 

 specialized parts. However, careful study shows that it really 

 consists of a single protoplasmic unit differentiated into cytoplasm 

 and nucleus. (Fig. 27.) 



The nuclear material in Paramecium, instead of forming a 

 single body as it does in most cells, is distributed in two parts: a 

 larger body, or macronucleus, and a smaller body, or micronu- 

 cleus. 1 Strictly speaking, the macronucleus and micronucleus 



1 The several species of Paramecium differ in regard to micronuclear number; 

 e.g., P. caudalum has one micronucleus, P. aurelia and P. calkinsi have two, and 

 P. polycaryum and P. woodrujji have several micronuclei. 



