The American Naturalist, Volume 43Essex Institute, 1909 - Biology |
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Page 18
... species , one northern , the other southern . Both are extremely variable and in their many forms and intergradations present to the taxonomist a problem of more than usual difficulty . Some features of the mor- phology of the northern ...
... species , one northern , the other southern . Both are extremely variable and in their many forms and intergradations present to the taxonomist a problem of more than usual difficulty . Some features of the mor- phology of the northern ...
Page 27
... species of Hedophyllum and to Agarum and Thalassiophyllum . Since from this standpoint the very young forms of Hedo- phyllum are not important , Setchell was not particular to obtain plants less than about 5 cm . in length . But for a ...
... species of Hedophyllum and to Agarum and Thalassiophyllum . Since from this standpoint the very young forms of Hedo- phyllum are not important , Setchell was not particular to obtain plants less than about 5 cm . in length . But for a ...
Page 56
... species which vary as A. tigrinum varies , are , after all , strongly determined by environing conditions . There is nothing new in this . But the study of this species seems to me to lend it new weight and confirmation . If the broad ...
... species which vary as A. tigrinum varies , are , after all , strongly determined by environing conditions . There is nothing new in this . But the study of this species seems to me to lend it new weight and confirmation . If the broad ...
Page 62
... species , and in 1850 Diesing recorded 81 cer- tain and 28 questionable species . Von Linstow's Compendium der Helminthologie and Nachtrag in 1889 gave references to 230 bird cestodes from 340 host species . In this investigation Fuhr ...
... species , and in 1850 Diesing recorded 81 cer- tain and 28 questionable species . Von Linstow's Compendium der Helminthologie and Nachtrag in 1889 gave references to 230 bird cestodes from 340 host species . In this investigation Fuhr ...
Page 63
... species and in genera . On the other hand , related birds of different food habits often show similar genera among their cestode guests even though the species differ . A zoogeographic survey of the cestodes in the various groups of ...
... species and in genera . On the other hand , related birds of different food habits often show similar genera among their cestode guests even though the species differ . A zoogeographic survey of the cestodes in the various groups of ...
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absence adaptation American animals appear bees breeding brown cells cent chromosomes corn plant correlation crinoids crossed curve Darwin dk.br dominant ecology eggs elementary species environment evidence evolution experimental experiments fact factors fertilization flowers fluctuating forms gametes genus green growth gynandromorphs hair color heredity heterozygote hybrids important index number individuals inheritance insects kelps L. H. BAILEY lamina large number larva larvæ Lessoniopsis lt.br male Mendelian Mendelian inheritance methods morphology muscular articulations mutation natural selection Notes and Literature observed offspring organs origin Origin of Species oyster pairs pangen paper Paramecium parent physiological pigment pinnule present problem produced Professor pure race RAYMOND PEARL rays Recapitulation Theory recent region relation Science seems selection index single sired specimens sporophytic stipe structure T. H. MORGAN theory tion unit characters variability variations varieties vegetation Vries yellow
Popular passages
Page 78 - But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position — namely, at the close of the Introduction — the following words : " I am convinced that natural selection has been the main but not the exclusive means of modification.
Page 156 - If numerous species, belonging to the same genera or families, have really started into life at once, the fact would be fatal to the theory of evolution through natural selection.
Page 69 - No man would ever try to make a fantail till he saw a pigeon with a tail developed in some slight degree in an unusual manner, or a pouter...
Page 135 - We are thus brought to the question which has been largely discussed by naturalists, namely, whether species have been created at one or more points of the earth's surface. Undoubtedly there are very many cases of extreme difficulty, in understanding how the same species could possibly have migrated from some one point to the several distant and isolated points, where now found. Nevertheless the simplicity of the view that each species was first produced within a single region captivates the...
Page 81 - Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part differs, more or less, from the same part in the parents.
Page 79 - One of the most remarkable features in our domesticated races is that we see in them adaptation, not indeed to the animal's or plant's own good, but to man's use or fancy.
Page 377 - ... 1 Papers from the Biological Laboratory of the Maine Agricultural Experiment Station. No.
Page 141 - The direct action of changed conditions leads to definite or indefinite results. In the latter case the organisation seems to become plastic, and we have much fluctuating variability. In the former case the nature of the organism is such that it yields readily, when subjected to certain conditions, and all, or nearly all the individuals become modified in the same way.
Page 138 - ... to natural selection, by affording a better chance of the occurrence of profitable variations. Unless such occur, natural selection can do nothing. Under the term of " variations," it must never be forgotten that mere individual differences are included.
Page 77 - There are, however, some who still think that species have suddenly given birth, through quite unexplained means, to new and totally different forms: but, as I have attempted to show, weighty evidence can be opposed to the admission of great and abrupt modifications. Under a scientific point of view, and as leading to further investigation, but little advantage is gained by believing that new forms are suddenly developed in an inexplicable manner from old and widely different forms, over the old...