An Introduction to the study of the protozoa with special reference to the parasitic forms / by E.A. Minchin.
- Minchin, Edward Alfred.
- Date:
- 1912
Licence: In copyright
Credit: An Introduction to the study of the protozoa with special reference to the parasitic forms / by E.A. Minchin. Source: Wellcome Collection.
Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.
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![understood. The term Protista thus unites under a single systematic category the vast assemblage of simple and primitive livint^ beings from which the animal and. vegetable kuigdoms have taken origin, and have developed, by a continuous process of natural evolution, in difierent dkections in adaptation to divergent modes of life. The conception of a Protistan kingdom separate from the animal and vef^etable kingdoms is open to the objection that it contains organisms which are indubitably of animal or vegetable nature respectively. The relations of the Protista to other living things may be repre- sented graphically by the accompanying dia- gram (Fig. 1), where the circle represents the Protista, the two triangles the animal and vegetable kingdoms respectively. It is seen that the separation of the Protista as a systematic unity cuts across the ascending series of evolution ; to express it figuratively, it is a transverse cleavage of the phylogenetic tree. A truly natural classification of living things, however, is one which expresses their genetic affinities and follows their pedigrees and lines of descent; it should represent a vertical cleavage of the ancestral tree. Judged by this standard, the kingdom of the Protista can only be regarded as a convenient makeshift or compromise, rather than as a solution of a Pro. 1 difficult problem—that, namely, of givmg a natural classification of the most primitive forms of life. Graphic representa- tion of the relation of the animal and vegetable king- doms to the kingdom of the Protista (Protisienreich). The Protozoa are represented by the portion of the triangle representing the animal ]?ingdom which lies within the circle representing the Protista. Whether the kingdom Protista be accepted or not as a natural and valid division of living beings, it is imperative to subdivide it further, not only on account of its vast extent and unwieldy size, but also because it comprises organisms very diverse innatiire, requiring for their study the application of methods of technique and investigation often entirely different in kind. Hence in actual practice the Protista are partitioned among at least three different classes of scientific workers—zoologists, botanists, and bacteri- ologists—each studying them by special methods and to some extent from different points of view. It is necessary, therefore, to consider from a general standpoint the principal types of organization comprised in the kingdom Protista, and we can recognize at the outset two chief grades of Structure, bearing in mind always that transitional forms between them must exist, or at least must have existed. In the first grade, which is represented by the Bacteria and allied groups of organisms, a type of organization is found which is probably the more primitive, though by many regarded as the](https://iiif.wellcomecollection.org/image/b22651822_0021.jp2/full/800%2C/0/default.jpg)
