THE STRUCTURE OF PROTOPLASM 
internal environment, using the latter term to refer, for example, to foods 
and wastes dissolved in the vacuolar cell sap. 
With this understanding as to definitions, I shall use the word cell as 
referring to the whole protoplasmic life unit, including the wall or envelopes 
of every kind. This will include in the cell conception multinucleated 
coenocytes and plasmodia as well, though it is obvious that here the content 
of the term is stretched until its usefulness becomes impaired. Still, I may 
note without discussion that this, in my opinion, is much better than to 
regard coenocytes and plasmodia as non-cellular or as tissues with cell walls 
omitted, as many do. We have here a case of which there are so many, 
where nature simply mocks our categories and shows the weakness of at- 
tempts to separate by definition objects that are so intimately connected 
in their evolutionary history. 
If, as I have suggested above, the visible organization, its architecture, 
is the structure of the protoplasm, we are confronted with the further sig- 
nificant consideration, which the numerous studies on the algae, fungi, 
and all the invertebrate phyla which have appeared in the last two decades 
have brought out very clearly, that this organization of the cell is every- 
where broadly speaking the same. From the one-celled alga or fungus to 
the highest plant or animal, the differentiation of nucleus, cytoplasm, 
chromosomes, spindle fibers, etc., is everywhere present, and in their general 
nature and functions and in their essential interrelations these structures 
ai*e the same. I am not overlooking the fact that nuclei have not been 
satisfactorily proved to exist in the bacteria, or that the central body of the 
blue green algae can perhaps best be considered as only a very aberrant 
form of nucleus. The macro- and micro-nuclei of the infusoria also imply 
a quite different type of organization from that of the common uninucleated 
cell. We must not, however, allow ourselves to be blinded by these 
facts, significant as they are and fruitful as they may become in deepening 
our conceptions of cell organization, to the great outstanding fact that 
evolution as we know it has not consisted in the production of new types 
of protoplasmic structure or cellular organization, but in the development 
of constantly greater specialization and division of labor between larger 
and larger groups of cells. The obviousness of this fact is brought out most 
conspicuously by the diagrams of a typical cell. Whether taken from the 
text-books of botany or zoology, these schematic figures all show a striking 
agreement as to the more fundamental structural features of a so-called 
typical cell. The differences between plants and animals, or between 
Pleurococcus and the pine, are not indicated primarily in the general or- 
ganization of their cells. 
We shall see most clearly the difference between the former and the 
new viewpoints when we note the disappearance of the old corpuscular 
theories of protoplasmic structure from the literature of present-day cytol- 
ogy. To explain certain evidences of the transmission of acquired characters 
