Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/84

58 hours’ incubation be folded in the same manner, its margin at many points is found to be no longer dark and even, but to be composed of extremely pale transparent cells. These cells present every variety of size, some being as large and even larger than the primitive globules of the germinal membrane. They either project forward in the form of half-spheres, or the greater portion of their spherical surface juts out in some instances, and they may be completely separated by pressure. They contain a pellucid fluid, but no nucleus. The following fact shows them to be cells; some of them contain very minute, isolated, black granules, which resemble the molecules described by Brown, and exhibit molecular motion within the cell. This fact proves that the contents of the cell must be fluid. A fluid which is miscible with water cannot, however, preserve any definite form, unless it be encompassed by a membrane. Such a structure must, therefore, exist in this instance. It is not altogether easy to convince one’s self that these granules, exhibiting molecular motion, do actually he within the cells; but it may be concluded from the fact, that they do not flow away when the surrounding fluid is allowed to escape, and that they are not moved beyond the limits of the cell, but only to its wall and back again. Beneath this stratum of cells le the globules of the unincubated germinal membrane, which, however, appear to have become still more clear and minutely granulous than those of the membrane examined after four hours’ incubation. In addition to these, separate cell-nuclei may be observed, such as occur in the cells of the serous layer at a subsequent period, and may be seen in plate II, fig. 6. Still more internally than this layer, we meet with perfectly dark globules. The serous and mucous layers of the germinal membrane are perfectly formed in the egg after sixteen hours’ incubation. If the membrane at that period be folded so that its external surface may be seen, it will be found