STRUCTURE AND DIVISION OF ORGANIC CELL. 815 



ing the formation of the memtrane 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 achroraatin-spindle, after the chromatin has aggregated at the 

 poles, and also of the chromatin-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 aggre- 

 gations of masses of chromatin. But the achromatin-stria3 of the nu- 

 clear 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 trans- 

 formation 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 hody^ 

 while the other nucleus retreats to the center of the ovum. The pro- 

 cess is precisely analogous to ordinary cell-division, the difference be- 

 ing 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 in- 

 teresting paper, descriptive of vegetable-cell division. His observa- 

 tions 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 in- 

 variably 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 



