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animals anterior appear asymmetry become biology body border cells cent changes chromosomes combinations component condition cones considerable considered cytoplasm days after operation described differentiation digits direction division dorsal dorsoventral double early ectoderm effect elements embryo evidence experiments fact factors fibers figure formation four function gills graft ground substance half hand increase indicate individuals kidney later less light limb bud lines material nature normal nucleus observed occurs organ orientation original Paramecium pigment plants points portion position possible posterior present preserved primary probably pronephros question reduplicating regard region relation remaining removed represent respect retina reversed right limb rods shown side similar single slightly species specimen stage stain structure surface takes theory third tion tissue transplanted ventral visual whole wound
Strona 272 - One has but to study his splendid series of illustrations to realize how animal development was placed upon a plane so advanced that for over a century it was unappreciated. One conclusion of Malpighi, however, was seized upon by contemporary biologists. Apparently, unbeknown to him, some of the eggs which he studied were slightly incubated so that he thought traces of the future organism are preformed in the egg. This error, coupled, for example, with Swammerdam's observation of the fact that parts...
Strona 280 - As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.
Strona 278 - Fifthly, from their first rudiment, or primordium, to the termination of their lives, all animals undergo perpetual transformations; which are in part produced by their own exertions in consequence of their desires and aversions, of their pleasures and their pains, or of irritations, or of associations; and many of these acquired forms or propensities are transmitted to their posterity.
Strona 259 - I frequently and seriously bethought me and long revolved in my mind, what might be the quantity of blood which was transmitted, in how short a time its passage might be effected, and the like.
Strona 254 - But any one who is practically acquainted with scientific work is aware that those who refuse to go beyond fact, rarely get as far as fact ; and any one who has studied the history of science knows that almost every great step therein has been made by the
Strona 254 - It is a favorite popular delusion that the scientific inquirer is under a sort of moral obligation to abstain from going beyond that generalization of observed facts which is absurdly called Baconian induction.
Strona 280 - ... the transmutation of species in itself disproved by the best physiological reasonings, but the additional assumptions which are requisite, to enable its advocates to apply it to the explanation of the geological and other phenomena of the earth, are altogether gratuitous and fantastical. Such is the judgment to which we are led by the examination of the discussions which have taken place on this subject. Yet in certain speculations, occasioned by the discovery of the Sivatherium, a new fossil...
Strona 182 - Average for 8 yrs. 634 1.74 reorganization of the cell (endomixis) without the cooperation of two animals involving syncaryon formation (amphimixis) as in conjugation. After endomixis was worked out, it seemed unnecessary to continue longer the main pedigreed culture and accordingly on May 1, 1915, at the 5071st generation, the experiment was formally considered as closed. The record of divisions for each year of the life of the culture to May 1, 1915, may be tabulated as shown in the preceding table....
Strona 260 - It seems not improbable, but that by these helps the subtilty of the composition of Bodies, the structure of their parts, the various texture of their matter, the instruments and manner of their inward motions, and all the other possible appearances of things, may come to be more fully discovered...
Strona 259 - ... from the arteries into the veins, and so return to the right side of the heart; I began to think whether there might not be a MOTION, AS IT WERE, IN A CIRCLE. Now this I afterwards found to be true; and I finally saw that the blood, forced by the action of the left ventricle into the arteries, was distributed to the body at large, and its several parts, in the same manner as it is sent through the lungs, impelled by the right ventricle into the pulmonary artery, and that it then passed through...