Zoology : an elementary text-book / [Sir A.E. Shipley].

  • Arthur Shipley
Date:
1904
Catalogue details

Licence: In copyright

Credit: Zoology : an elementary text-book / [Sir A.E. Shipley]. Source: Wellcome Collection.

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    entirely new character arises. Such deviations of the offspring from the average of the parents constitute variation. If the difference is striking the individual exhibiting it is called a sport. It is obvious that so vast a science as Zoology must be divided into various branches, since the different questions ofzooiogy. if seeks to solve require that special attention should be given to each side of the subject. Thus, the nature and conditions of the metabolism and the mechanism by which movements are effected, etc., constitute the subject-matter of Physiology; the investigation of the structure of individuals and of the differences in structure between the various species and the search for the causes of these differences is termed Morphology; whilst Bionomics is the name given to the study of the means whereby an animal obtains its food and orders its life, in other words, of its habits. But it must be remembered that all such divisions are purely arbitrary, and indeed no great progress can be made in any one department if the others be ignored. Bionomics, when followed to its sources, passes into Physiology, and in trying to explain the different structures studied in Morphology constant recourse must be had to bath Physiology and Bionomics. Of all divisions of the subject, that of Physiology has been most neglected; it has indeed only been studied systematically in the case of man and of a few of the higher animals. Hence this work will be mainly concerned with the questions of Morphology and Bionomics. Of these questions, by far the greatest is the problem how the distinctions between the various species are to be explained. The question of the “ Origin of Species ” involves nearly all others in Zoology. The distinctions between species are of very different degrees, classification s0 ^at ^or convenience species closely resembling each other are collected into genera—genera into families—families into orders—orders into classes—and classes into phyla. These are the names in commonest use, but often the nature of the subject requires the introduction of further grades of difference, and the number of grades actually employed depends to a large extent on the point to which the analysis is pushed. The only theory of the origin of species which has so far commanded any considerable agreement amongst ofSpecies. naturalists is the famous theory of Charles Darwin. According to this theory, the resemblances between a number of living species are due to the fact that these species
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