Introduction To The Syudy Of Biology


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Seite 53 - We come to a still more extraordinary part of the imitation, for we find representations of leaves in every stage of decay, variously blotched, and mildewed, and pierced with holes, and in many cases irregularly covered with powdery black dots, gathered into patches and spots, so closely resembling the various kinds of minute fungi that grow on dead leaves, that it is impossible to avoid thinking at first sight that the butterflies themselves have been attacked by real fungi.
Seite 57 - The sub-kingdoms are, in turn, broken up into classes, classes into orders, orders into families, families into genera, and genera into species.
Seite 19 - But it must be said that there are organisms which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as animals, whilst at another they appear to be as distinctly vegetable.
Seite 135 - Until recently the great majority of naturalists believed that species were immutable productions. and had been separately created. This view has been ably maintained by many authors. Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre-existing forms.
Seite 49 - When identical or nearly similar forces, or environments, act on two or more parts of an organism which are exactly or nearly alike, the resulting modifications* of the various parts will be exactly or nearly alike. Further, if, instead of similar parts in the same organism, we suppose the same forces to act on parts in two organisms, which parts are exactly or nearly alike and sometimes homogenetic, the resulting correspondences called forth in the several parts in the two organisms will be nearly...
Seite 61 - Upon the whole, then, it seems in the meanwhile safest to adopt a definition of species which implies no theory, and does not include the belief that the term necessarily expresses a fixed and permanent quantity. Species, therefore, may be defined as an assemblage of individuals which resemble each- other in their essential characters, are able, directly or indirectly, to produce fertile individuals, and ivhich do not (as far as human observation goes) give rise to individuals u-hich vary from the...
Seite 57 - No term is more difficult to define than " species," and on no point are zoologists more divided than as to what should be understood by this word. Naturalists, in fact,' — so he extends the remark beyond the limits of zoology, — ' are not yet agreed as to whether the term species expresses a real and permanent distinction, or whether it is to be regarded merely as a convenient, but not immutable, abstraction, the employment of which is necessitated by the requirements...
Seite 17 - ... even in the process of digestion as exhibited in the Amoeba there is something that is not merely physical or chemical. Similarly, any organism when just dead consists of the same protoplasm as before, in the same forms, and with the same arrangement ; but it has most unquestionably lost a something by which all its properties and actions were modified, and some of them were produced. What that something is we do not know, and perhaps never shall know ; and it is possible, though highly improbable,...
Seite 59 - Distinctions which appear to one observer as sufficiently great to entitle the individuals possessing them to be grouped as a distinct species, by another are looked upon as simply of varietal value; and, in the nature of the case, it seems impossible to lay down any definite rules. To such an extent do individual differences sometimes exist in particular genera — termed " protean " or " polymorphic " genera — that the determination of the different species and varieties...
Seite 58 - Quatrefages defines species as "an assemblage of individuals, more or less resembling one another, which are descended, or may be regarded as being descended, from a single primitive pair by an uninterrupted succession of families." Miiller defines species as "a living form, represented by individual beings, which reappears in the product of generation with certain invariable characters, and is constantly reproduced by the generative act of similar individuals.

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