Сторінка:Труди фізично-математичного відділу. Том II. Вип. 2-5. 1926.pdf/435

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the conclusion aught to be made, that on its whole length the lateral plate is, at a certain period, so determined, that under the influence of an irritator it can form a limb.

As it could be supposed, that the character of this irritation must be more or less simple, I tried whether by simply wounding the lateral plate limb-induction could be produced. This experiment gave an altogether negative result.

What is the material, that forms the capsule-cartilages, if the sideplate is specific? In this respect the cartilages may be divided into two groups. In the first group it may be traced, that the capsules are built from the axial mesenchym, that is derived from the sclerotoms. In № 80 (1924) the material, that aught to have built ribs, has been used up for the capsule; in № 61 (1924) the cartilage of the capsule forms a whole with the cartilage ot the axial skeleton. Thus the axial mesenchym on its whole length can form an ear-capsule under the influence of the ear vesicle.

In the second group (№№ C-9, C-10, C-18, C-28, 1925) it is quite clear, that the capsule cartilages are formed of the same material, as the limb cartilages, that is, from the material of the lateral plate.

Thus it follows, that the lateral plate at the same time consists of specific material, and of material that is so far indifferent, that it can be used for capsule-formation. It may be, that the determination does not take place at the same time for all the cells forming the lateral plate, and at a certain moment there are both determinated and undeterminated cells. But then we must expect, that the relation between the mass of the capsule cartilages and the limb-cartilages must be the same in larvae operated in a certain stage, also the capsule cartilages must prevail in earlier operated larvae and the limb-cartilages in larvae operated later. In my experiments this is not so: the capsule-element is sometimes more prevailing in cases operated later, than in cases operated earlier.

I find, that another explanation should better suit my exprimental results. The determination is not a simultaneous process. The experiments of Gräper, Harrison and Brandt show, that there are at least two stages of determination: 1) when the determination is not yet irrevocable and a redetermination may take place 2) when the determination is quite irrevocable. This gives the impression, as if the determination is, at least to a certain point, a quantitative process. I suppose, that the determination of all the cells of the lateral plate happens at the same time. But the influence of the ear vesicle may produce a redetermination. This redetermination may happen in a part of the cells of the lateral plate on which the influence of the ear vesicle was the strongest; at the same time the determination of other cells may remain unchanged, their potencies may be activated, and they may form an induced limb.

In one case, № 28 (1925), a limb bud had appeared, but was later nearly quite reduced. There was no trace of necrobiosis or phagocytosis in