Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/211

SURVEY OF CELL-LIFE. 185 place before the cell-wall and cell-cavity exist as distinct structures, somewhat in the following manner: the nuclei are formed first, around them a new stratum of substance is deposited, the external portion of which, in accordance with the course of formation of an ordinary simple cell, would become condensed into a cell-membrane. But in this instance the nuclei lie so close together, that the strata forming around them and corre- sponding to the cells, flow together, to form a cylinder, the ex-lternal portion of which becomes condensed into a membrane, just in the same manner as in simple cells, where merely the external portion of the stratum formed around the nucleus, becomes hardened on the outside into a membrane, in consequence of the reception of new molecules. There is, therefore, nothing in this which differs so very materially from the course of development of a simple cell; indeed, we seemed to be compelled to assume a similar process for the formation of the nuclei furnished with two or more nucleoli. (See page 176.) It is possible that there may be stages of transition between the ordinary simple cell and these secondary cells. It has been already mentioned at pages 117-118, that fat-cells occur in the cranial cavity of fishes, many of which contain two nuclei. It is possible that only one of them is the cytoblast of the cell, and that the second is a nucleus which has formed subsequently; but they resemble one another so completely in their characteristic position on the cell-membrane (see pl. III, fig. 10,) that perhaps they may both be cytoblasts of a cell which has been formed around both nuclei, in consequence of the external stratum of the precipitate having become condensed in such a manner that the membrane enclosed both nuclei. Meanwhile observation affords no demonstrative proof on the subject, and the similarity in the position of these two nuclei may be explained in another way. Fat thrusts all bodies which have imbibed water towards the outside of the cell, in order that it may assume its own globular form. If now a second nucleus should form in one of these fat-cells, it will be thrust towards the outside, and must gradually raise the cell-membrane into a prominence. It may also be observed, that opportunities of demonstrating the actual absorption of the fully-developed partition-wall between two cells do occur in the spiral vessels of plants.