38 THE CELL DOCTRINE. 



ent from the above-described, is exhibited in the 

 multiplication of cells by division of the existing 

 ones; in this case, partition-walls grow across the old 

 cell, if, as Schleiden supposes, this be not an illusion, 

 inasmuch as the young cells might escape observa- 

 tion in consequence of their transparency, and at a 

 later stage, their line of contact would be regarded 

 as the partition-wall of the parent cell." 



It would be easy to point out other defects in the 

 theory of Schleiden and Schwann, when it is tested 

 by comparison with the more accurate observation 

 of the last twenty-five years, none of w T hich should 

 be permitted to detract from the credit which at- 

 taches to the originators of this conception. It must 

 not be forgotten, that it is no less true of science than 

 of art, that great and important truths in their en- 

 tirety, are gradually' developed, and that no single 

 mind is capable of elaborating them from their in- 

 cipiency to their complete expression. And, since 

 many clever people had daily noticed the rising of 

 steam from the boiling kettle without thinking of 

 utilizing its principle of expansion, so many careful 

 observers had time and again witnessed the cellular 

 or vesicular composition of plants, and yet failed to 

 appreciate the importance of the nucleated cell, and 

 to deduce from it a law of development applicable to 

 all organic forms. Again, as the engine of Watt 

 was far different from the beautiful and powerful 

 creation of the mechanic of the present day, so the 

 cell theory, as developed by Schleiden and Schwann, 

 has been further evolved by later histologists. So 

 that we may truthfully reiterate, with Prof. Huxley, 



