Contributions to Education, Utgåva 65


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Sida 24 - All modifications and variations in progressive series tend to appear first ,in the adolescent or adult stages of growth, and then to be inherited in successive descendants at earlier and earlier stages according to the law of acceleration, until they either become embryonic or are crowded out of the organization and replaced in the development by characteristics of later origin.
Sida 25 - The acceleration in the assumption of a character, progressing more rapidly than the same in another character, must soon produce, in a type whose stages were once the exact parallel of a permanent lower form, the condition of inexact parallelism.
Sida 25 - Where characters which appear latest in embryonic history are lost, we have simple retardation — that is, the animal in successive generations fails to grow up to the highest point, falling farther and farther back, thus presenting an increasingly slower growth in this special respect.
Sida 26 - ... living species, should be inclined to discredit the law of tachygenesis, and to believe that there is such an inextricable muddle of omissions, secondarily introduced characters, and unequal acceleration of those actually repeated, that the record is wholly untrustworthy, or at least illegible. And yet there are so many species and genera in the various groups of invertebrates whose ontogeny is simple, progressive and fairly complete, and whose stages of growth are almost exact repetitions of...
Sida 13 - As the embryo often shows us more or less plainly the structure of the less modified and ancient progenitor of the group, we can see why ancient and extinct forms so often resemble in their adult state the embryos of existing species of the same class.
Sida 14 - The historical record preserved in developmental history is gradually effaced as the development strikes into a constantly straighter course from the egg to the perfect animal, and it is frequently sophisticated by the struggle for existence which the free-living larvae have to undergo. "Which of the different modes of development at present occurring in a class of animals may claim to be that approaching most nearly to the original one, is easy to judge from the above statements." 18 9. "Ontogeny...
Sida 13 - On the other hand it is highly probable that with many animals the embryonic or larval stages show us, more or less completely, the condition of the progenitor of the whole group in its adult state.
Sida 21 - This conception of a tree, symbolizing the relationships of types and a species derived from the same root, has a concomitant conception. The implication is that each organism, setting out from the simple nucleated cell, must in the course of its development follow the line of the trunk, some main branch, some sub-branch, some sub-sub-branch, etc., of this embryological tree; and so on till it reaches that ultimate twig representing the species of which it is a member. It must in a general way go...
Sida 14 - ... nothing. In the second case the entire development of the -progenitors is also passed through by the descendants, and, therefore, so far as the production of a species depends upon this second mode of progress, the historical development of the species will be mirrored in its developmental history. In the short period of a few weeks or months, the changing forms of the embryo and larvae will...
Sida 47 - In short, how much liberty has any phase of growth to evolve by itself without markedly disturbing other phases? The facts, as reported by the investigators, seem to favor the suggestion of Cumings. Thus in the language of Driesch, "... .the actual fate of a part need not be identical with its possible fate, at least in many cases;.. .. There are more morphogenetic possibilities contained in each embryonic part than are actually realized in a special morphogenetic case.

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