HISTORY OF PROTOZOOLOGY Protozoa were first discovered in the latter half of the 17th century by A. van Leuwenhoek (1632-1723) a Dutch amateur naturalist and chamberlain to the sheriff of Delft. Leuwenhoek carried on his investigations with magnifying glasses and micro scopes he had designed and made himself.
A systematic investigation and description of all known Proto zoa was undertaken for the first time by the Dane, 0. F. Muller (173o-84). In the 19th century C. G. Ehrenberg, professor of zoology in Berlin (1795-1876), tried to show that Protozoa had an organization similar to that of the higher organisms. This attempt failed because Ehrenberg's scientific opponent, the Frenchman Dujardin, was able to demonstrate the unicellularity (in essence at least) of the Protozoa. The fact that Protozoa were unicellular was enunciated by the German zoologists M. Schultze (1861) and von Siebold. In the era of Darwinism the Protozoa were principally looked at from the point of view of the evolutionary theory; in them were seen the root-forms of the higher animals. Later on protozoans were recognized as causers of disease ; the first pathogenic protozoan, Nosema bombycis, was discovered by Pasteur. The greatest advance in the study of pathogenic Protozoa began with the investigation of the Nagana cattle plague by David Bruce; by showing that this disease was caused by Trypanosoma brucei he opened a new era of activity in protozoological research which has carried us on to the present day. In this period the study of the body-structure, life-cycles and physiology have equally received attention. Amongst these the classical researches of the Englishman Ronald Ross and of the Italian B. Grassi deserve special mention, on account of their achievement with malaria, also the work of the German F. Schaudinn (1877-1906) on the life-cycle of the Coccidia and of many other Protozoans especially in regard to cytology.
We have already mentioned the fact that the different forms of life included under the name Protozoa do not show the same rela tionships as the different classes that we recognize amongst the vertebrates; indeed that many of them cannot be shown to have any relationship whatever with one another. This is true for some,
but not for all, classes and orders of the Protozoa; some of these, such as the Flagellata, Protomonadina, Rhizopoda, Heliozoa, are not to be regarded as natural groups at all. They are convenient assemblages of organisms not demonstrably related.
We divide the Protozoa into five great classes:— I. Mastigophora (Flagellata) 2. Rhizopoda 3. Telosporidia 4. Neosporidia 5. Ciliophora (Infusoria) It should be clearly understood that (I) and (2) are both unnatu ral groups.
I. Order Chrysomonadina. Very small autotrophic flagellates; one or two flagella; always free-living, in fresh and salt water; the chromatophores usually contain a brown pigment. The cyst, furnished with plugged hole, is characteristic of many Chryso monadina; its membrane contains silicic acid. Unicellular and uninucleate ; reproduction by simple fission; fertilization processes are only known in a few forms. A very large order in the number of its species; the most important family is the Coccolithophori dae consisting of marine chrysomonad:nes, which have shells com posed of chalk disks and are important as food for many plankton organisms. Important types : Chromulina, Ochromonas, Dino bryon, Syracosphaera.