. The biology of the protozoa. Protozoa; Protozoa. 22 BIOLOGY OF THE PROTOZOA For such colonies of protozoa, as for analogous colonies of hydroids, the expression "individual of a second order" has been applied. Between the limits of the simplest and the most complex of uni- cellular organisms are the great majority of the (estimated) 15,000 or more known Protozoa. In each of the main subdivisions sim- plicity as well as extreme complexity of organization is represented, each subdivision including a series of representative forms ranging from one extreme to the other. Differentiation
. The biology of the protozoa. Protozoa; Protozoa. 22 BIOLOGY OF THE PROTOZOA For such colonies of protozoa, as for analogous colonies of hydroids, the expression "individual of a second order" has been applied. Between the limits of the simplest and the most complex of uni- cellular organisms are the great majority of the (estimated) 15,000 or more known Protozoa. In each of the main subdivisions sim- plicity as well as extreme complexity of organization is represented, each subdivision including a series of representative forms ranging from one extreme to the other. Differentiation in the different subdivisions do not follow the same lines of development, however, so that we are able to classify Protozoa according to a fairly natural system. These diverse lines of development make it difficult to treat this branch of the animal kingdom in any general way; the wide range in habitat from the purest waters of lake or sea to the. Fig. 3.—Types of Protozoa. A, Amoeba proteus, a rhizopod; B, Peranema tricho- phora, a flagellate; C, Stylonychia mytilis, a ciliate; D, a polycystic! gregarine; E, Tokophrya quadripartita, a suctorian. (A, after Calkins, B, C, E, after Butsehli; D, after Wasielewsky.) foulest ditch, and adaptations to environments varying in charac- ter from a mountain stream to the semifluid substance of an epithe- lial, nerve or muscle cell, has brought about manifold varieties of structure. To describe all of these modifications under a few headings, or to attempt to formulate general laws from the different and often highly complicated life histories, is out of the question. The general trends of differentiation, however, permit of grouping the different kinds of Protozoa in four types which were first out- lined by the French microscopist Felix Dujardin in 1841. Three of these types—Sarcodina, Mastigophora and Infusoria—are based upon the nature of the locomotor organs—pseudopodia, flagella and cilia respectively—while a fourth type
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