Evolution / by Patrick Geddes and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1911?]
Catalogue details

Licence: Public Domain Mark

Credit: Evolution / by Patrick Geddes and J. Arthur Thomson. Source: Wellcome Collection.

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    myxa and Myxomycetes, we get a new light on our classification. For in these life- histories we find, for instance, that amoeboid forms become encysted, that the encysted stage gives rise to active flagellate spores, and that these sink down again into amoebae. The three chapters in the life-history of the simplest forms are, as it were, prophecies of each of the three groups—Infusorians, Rhizo- pods, and Gregarines. In other words, the most primitive organisms pass through a cycle of three phases, one of which is accented by each of the three main groups of Protozoa. And while each main group is characterized by one dominant phase of cell-life—flagellate, amoe¬ boid or encysted-—there are often transient hints of other phases. An infusorian may have its encysted chapter, a gregarine its amoeboid stage, and a rhizopod may begin as a mobile flagellate spore; for each group, while accenting one phase of the cycle, retains reminiscences of the others. The conviction that the triple division really means much, grows stronger when we pass from the unicellulars to the cells that compose the higher animals. For they, too, may be rationally classified along the three great lines. There are active ciliated or flagellate cells in most animal types-—the flagellate cells of