equivalent in function to the aggregate of cells making up the metazoon, and with some parts at least having the power to contract and move, some to digest food, some to secrete, others to excrete and still others, finally, to reproduce. Considered in this sense the cell theory as applied Fig. 1.Original. to the Protozoa is obviously inadequate.
The especial portions of the protoplasm that have to do with these several different functions of the protozoon can be identified in many cases as structurally different from the remainder, especially those parts which have to do with movement and with the perpetuation of the race, i. e., the germ plasm. In the majority of Protozoa this portion of the protozoon is clearly differentiated, one time or another, from the remainder of the cell, and this justifies us in taking issue with Weismann, and with the majority of those who write casually about the Protozoa, as having no somatic cell elements and therefore no possibility of natural death. If it can be shown that there is a specific germ plasm in these unicellular animals, then the matter of immortality differs in no essential way from the same problem in Metazoa or Metaphyta where the germ cells have a possibility of endless existence. The evidence points to a common and universal law that continued life is an attribute of an especially endowed protoplasm, termed germ plasm, which forms the material basis of the reproductive cells.
The history of single Protozoa, if taken superficially, seems to point to the fact that the protoplasm of these cells does not die a natural death, but continues to live in successive generations of similar individuals.