/2 GENERAL PRINCIPLES OF ZOOLOGY. 



Schwann view, that the old name has been retained, 

 although it no longer at all fits the new conception. We 

 have indeed become so thoroughly accustomed to the 

 name that we no longer notice the contradiction of terms 

 when we call a solid lump without a membrane a "cell." 

 Discovery of Protoplasm. The reformation of the 

 cell theory was begun by discoveries which were made in 

 very different regions and only lately have been brought 

 to a focus. 



1. Already, at about the beginning of the nineteenth 

 century, Bonaventura Corti and Treviranus had seen that 

 the chlorophyl bodies, which cause the green color of 

 plants, in many species stream around in a lively manner in 

 the interior of the cell, but Mohl was the first to find out 

 that this motion is not active, but rather that they are 

 moved by a homogeneous substance in which they are 

 embedded. This substance, which Mohl, in order to 

 bring it into prominence, named protoplasnia, obtained by 

 a second observation still greater importance. In the case 

 of reproduction of the simplest algae, it was found that the 

 protoplasm, together with the chlorophyl bodies, balled 

 itself into an oval mass, and that this body left the cell mem- 

 brane and swam freely in the water. Since the cell-wall 

 no longer showed signs of life, while on the other hand the 

 protoplasmic body came to rest and formed a new plant, it 

 was shown beyond doubt that this was the most important 

 constituent part of the cell (comp. Fig. no). 



2. In the study of animal tissues the importance of the 

 peculiar cell-substance, the protoplasm, was still more 

 plainly brought out. Here, in spite of the long-prevailing 

 preconceived idea, unbiassed observation led to the dis- 

 covery that animal cells, in general, had no cell-mem- 

 brane. 



3. Very important finally was the study of the lowest 

 organisms, the protozoa. Dujardin sought by extremely 

 careful observations to adduce the proof that these animals 

 had no organs, but consisted of a uniform granular sub- 

 stance, the sarcodc. The sarcode alone could condition 



