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 are 

 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 facts in the biological world are not considered explained until they 

 have been reduced to terms of cell units. 



Not a living thing, plant or animal comes into existence which 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 the parts shown in this ideal cell. 



Lmin ^Vof-tUO-k — 



mm 



u *r h 



Fig. 26. An Ideal Cell, 



