PROGRESS IN PROTOZOOLOGY

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evidence for the assumption of polyphyletic origins of some of the large
assemblages of PROTOZOA. This lack of evidence provides good reasons
to regard the foregoing assumption with suspicion.
At present, the correct principles lie in the "Synthetic Theory of
Evolution," the modern version of Darwinism, which has been espoused
by a number of outstanding scientists (Huxley, M a y r, Dobzans
k y, and Schmallhausen, among others).
Among the principal lines of evolution of the main protozoan groups,
the central position is occupied by MASTIGOPHORA. Their assumption
of parasitic existence has resulted in the evolution of the large phylum
APICOMPLEXA, among which SPOROZOA are the most important.
Equally certain is the relationship between the flagellates and the most
advanced protozoan group, CILIOPHORA. The close relationship between
MASTIGOPHORA and SARCODINA (above all AMOEBINA) is
beyond a doubt. The question of which of the two assemblages originated
first has been answered differently by various authors; I do not
propose to consider the details of this controversy.
From all the foregoing, it follows that the question of whether the
PROTOZOA constitute a "natural" group should be answered in the
affirmative.
The PROTOZOA represent a step in the evolution of living organisms
characterized by unicellulairity and common origin. This statement is not
to imply that all PROTOZOA originated from a single "Archiprotozoon"
which appeared a very long time ago on our planet. Evolutionary events
concerned populations rather than a single organism. It is likely that
from the very beginning of life on our planet, evolution was directed
toward biocoenoses and to their component populations.
Although we may admit the reality and phylogenetic unity of the
subkingdom PROTOZOA, we cannot express a definite opinion as to the
evolutionary relationships among all the large protozoan taxa.
CNIDOSPORIDIA may have originated from metazoan ancestors in
the course of adaptation to tissue parasitism (L o m, among others). If
this hypothesis is valid, the inclusion of the cnidosporidians among
PROTOZOA is artificial. It is also unsafe to include MICROSPORIDIA,
with their aberrant cell structure, in this subkingdom. It is likely that
other smaller protozoan groups also have no phylogenetic relationships
with PROTOZOA. None of these facts alter my view that this subkingdom
constitutes a natural group which appeared in the course of organic
evolution on earth.
Among the discussants of the last section of the Round-Table Discussion,
Professor MICHAJLOW used species of the genera Euglena and
Astasia to show that formal divisions among various protozoan groups,
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