PROTOZOA 



I4i 



between the simplicity of Amoeba and the complexity of 

 Carchesium there is an immense number of animals whose 

 structure is non-cellular. 1 These animals are known as 

 Protozoa. Cellular animals are known as Metazoa. Those 

 Protozoa which move by means of pseudopodia are called 

 Rhizopoda, those which move by fiagella are Flagellata, 

 those which move by cilia are Ciliata. Protozoa which, 

 like Monocystis, have no 

 external organs of loco- 

 motion, are parasites, 

 and form numerous 

 spores, are known as 

 Sporozoa. In comparing 

 Amoeba with the frog we 

 noticed that the absence 

 in the former of cells — 

 that is, of energids in the 

 body which are specialised 

 and therefore liable to 

 natural death — led to its 

 being, in a certain sense, 

 immortal. The same is 

 true of all Protozoa, al- 

 though, as we shall see later, most Ciliata, in which there 

 is a partial separation of body-substance in the form of a 

 special nucleus, do at times purchase their immortality at 

 the price of the loss of the meganucleus, forming a new 

 one from the micronucleus. 



In the next chapter there will be found (p. 158) descrip- 

 tions of several Ciliata which are parasitic in the frog and 



Fig. 87. — A colony of Carchesium 

 under low magnification. 



1 They are often said to be unicellular, but this, as we have seen 

 (p. 120), is an illegitimate use of the term "cell." 



