THE CELL AND ITS STRUCTURE. 23 



of unicellular animals is often called) into long, ir- 

 regular projections, called pseudopodia, or false feet. 

 The use of them, is to move with, or to catch food, if 

 anything touches them. This animal is considered to 

 present the most generalized form of the animal cell, 

 from which all other forms are derived. Cells which 

 closely resemble it are spoken of as amoebiform. 



Most of the animals we are acquainted with consist 

 of a vast number of cells ; but some of the little ani- 

 mals that we can only see with the microscope con- 

 sist only of one cell; and every animal, in the first 

 stage of its existence, consists of only one cell, for 

 this is the primary form of the egg. ( See Chap. V.) 

 There are some animals which consist of more than 

 one cell, but not of very many ; when this is the case, 

 there is sometimes not much difference between the 

 various cells. But where there are a vast number, as 

 is the case with most animals, even very small ones, 

 we find that different groups of cells undertake some 

 special work of the animal body:; and in order to do 

 this, they become modified in some way that fits them 

 for the special purpose, whatever it is, so that they 

 assume a different shape and appearance from that of 

 the ordinary type of cell. 



Let us consider how many things there are for the 

 animal body to do. 



1. It has to breathe. 



2. It has to feed. 



3. It has to get rid of waste products. 



4. It has to grow. 



