CHAPTER V. 



THE CELL 



It will be observed later in the study of the histology of the frog 

 that the different types of cells vary in size and shape, some being round, 

 others more or less cuboidal, still others cylindrical, etc. As there are 

 animals possessed of but a single cell which can nevertheless perform 

 all acts necessary to a complete organism and, consequently, can lead an 

 independent existence, the cell is called the biological unit, and things 

 in the biological world are not considered explained until they have been 

 reduced to terms of cell units. 



There is not a living thing, plant or animal, which comes into ex- 

 istence that does not start life as a single cell. It is therefore an axiom 

 ( ) of science that there can be no living cell unless 



it sprang from a previous cell. Therefore, an egg, regardless of whether 

 it be the small egg of a frog or so large a one as that of the ostrich, is 

 only a single cell. In fact, in the hen's egg usually used in the laboratory 

 for experimentation, the yolk represents the food for the offspring, the 

 egg proper being that little portion, about the size of a dime, which 

 always floats on the top of the yolk, regardless of the position of the 



egg. 



The following drawing (Fig. 26) is that of an ideal cell. This means 

 that everything which the student will ever find in any cell, plant or 

 animal, is contained in this drawing. One must remember, however, 

 that search may be made from now until the end of time and no one cell 

 may ever be found with all of the parts shown in this ideal cell. 



Cll Htrnfc 



Fig. 26. An Ideal Cell. 



