Page:Popular Science Monthly Volume 26.djvu/835

Rh the formation of the membrane be correct, it may prove that the disks of the spindle-fibrils are the origin of the cell-wall, and that similar disks arise at the extremities of achromatin-fibrils in the new nuclei to form their membranes. And Pfitzner's observations would indicate that the fibrils are really composed of achromatin, upon which chromatin gathers either continuously or in separate spherules. In such a case the movements of chromatin would be along lines of achromatin; and we can comprehend the appearance of the lines of the achromatin-spindle, after the chromatin has aggregated at the poles, and also of the chrormatin-disks which are shown equatorially on these lines. The chromatin of the fibrils has aggregated at the poles and the equator of the nucleus, and left apparent intermediate lines of achromatin.

In vegetable-cell divisions Strasburger finds none of this regular process, but only a vague approach to it in the movements and aggregations of masses of chromatin. But the achromatin-striæ of the nuclear spindle, the equatorial plate, and the sun-like polar rays, are well declared. In some cases of abnormally rapid nutrition a threefold division takes place, and possibly a still greater number of new cells may be formed. The process of cell-budding may be similar to that above described, if we can judge from observations on the early transformation of the ovum. Here a nuclear spindle is formed, with its polar suns. This moves to the surface of the cell, and one of the poles is pushed out through its wall. Constriction takes place, and the new nucleus remains on the outer surface of the cell as the polar body, while the other nucleus retreats to the center of the ovum. The process is precisely analogous to ordinary cell-division, the difference being that one of the new nuclei retains around it all the substance of the original cell, while the other is destitute of it. Did this polar body become free, and grow by absorbing new nutriment, the resemblance to ordinary cell-budding would be complete. Frequently two or more polar bodies are thus formed ere fertilization of the ovum takes place. Possibly the cell buds off its male element and retains only its female. An analogous process takes place in the spermatozoa. It would seem as if the germinal cells were becoming specially male and female in energy ere combining to form the germ of a new individual.

Recently Mr. J. M. Macfarlane, of Edinburgh, has published an interesting paper, descriptive of vegetable-cell division. His observations were made on the cells of Spirogyra, a common fresh-water alga. The large nuclei of these cells seem specially adapted to observation. He found not only that the nucleolus was very distinct, but that it invariably contained a well-defined body, which he names the nucleolo-nucleus. He found this body in all plant-cells examined, and also in cerebellum-cells of animals. In staining with carmine the stain hardly affected the outer cell-substance, the nucleus took a somewhat deeper stain, the nucleolus was deeply colored, and the nucleolo-nucleus still