Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/83

Rh embryo is first formed, the germinal membrane. It represents, as is known, a round, white, little disc, somewhat above a line in breadth, which lies between the vitelline membrane and the yelk-substance. This little disc, in a fresh-laid hen’s egg, consists of globules, which are of unequal size in different parts of the germinal membrane. When examined with the microscope, they appear much darker than the yelk-globules, (see plate II, fig. 4.) They lie in close contact, so that they flatten against one another to an hexagonal form. The boundaries of the distinct globules may be clearly distinguished, even when in connexion. They may also be readily isolated from one another, and are then round. They contain many smaller round granules of various size, with very dark outlines, which float about singly when the globules are burst by pressure. Although these granules, in most instances, completely fill the globules, yet some globules may be observed where that is not the case, and where a portion of the globule is transparent, and free from granules, (a b, of the above figure.) I thought that I distinctly saw a double external outline on one of these globules (a), which would be evidence of the presence of a cell-membrane. In most instances, however, this is not distinct, and my principal reason for concluding that they are cells, is, that it is so extremely probable that they are developed to form the indubitable cells of the incubated germinal membrane. I have not, however, fully investigated this process, and only communicate my observations on the point, incomplete as they are. If the unincubated germinal membrane be folded in such a manner that its external surface form a sharp margin, that surface is found to be tolerably even, dark, and composed immediately of the globules of the germinal membrane already described; the surface of the germinal membrane of an egg which has been exposed to brooding heat for four hours, presents a precisely similar appearance. The same membrane, when examined also upon its general surface, differs but very slightly in appearance from one which has not undergone incubation. The globules of which it consists merely appear to have more minutely granulous contents. But if a germinal membrane after eight