288 ' Walker and Einbletoii 



purple with method A, and bright red, sometimes with a blue area in the 

 centre, with method B. They may frequently be seen to be budding in a 

 manner very like the budding of the nucleoli in nerve-ganglion cells 

 described elsewhere.^ 



In both endoderm and ectoderm cells the budding often takes the form 

 of a small excrescence which gradually separates from the nucleolus, 

 remaining joined to it, however, for a considerable period by a membranous 

 process (see tigs. 1, 2, and 8). Sometimes, however, particularly in the 

 cells of the endoderm, the nucleoli seem to divide more or less equally from 

 the beginning, and it is impossible to describe this form of division as 

 budding. Very often there is one large nucleolus to be seen and several 

 small ones (fig. 2), but we also find some nuclei containing two or more 

 large nucleoli nearly equal in size (fig. 4). Nucleoli may also frequently 

 be seen in process of passing through the nuclear membrane. As the 

 nucleolus passes through, the nuclear membrane appears to form an 

 encircling lip round it, the membrane being re-formed underneath it 

 very rapidly (figs. 5 and 6). Thus, when the nuclear membrane has 

 re-formed behind the extruded nucleolus, the latter lies in a depression not 

 unlike a crater. Almost as soon as the nucleolus has passed through the 

 membrane, the dark purple colour it exhibits when stained by method A 

 is lost at its periphery, leaving this pink. We thus have a spherical 

 nucleolus with a dark purple area in the centre, surrounded by an area 

 stained pink (figs. 1, 4, 7, 8, and 9). The purple centre appears to 

 decrease rapidly, leaving the nucleolus pale pink throughout. With 

 method B the blue or violet area seen in some nucleoli while within the 

 nucleus is lost as the former passes into the cytoplasm. In every case the 

 nucleolus becomes more and more orange in colour as it leaves the 

 neighbourhood of the nucleus. In the cells of the endoderm, nucleoli may 

 often be seen in process of division, after they have been extruded from the 

 nucleus. It seems that after this, in the endoderm cells, the nucleoli are 

 pushed towards the periphery of the cytoplasm. On approaching the 

 periphery they lose the pink colour (obtained with method A) and take 

 the orange stain, becoming at the same time much less defined, and appear 

 eventually to disintegrate altogether. 



We have been unable hitherto to trace the destiny of the nucleoli in 

 the cells of the ectoderm after their extrusion. Occasionally the nucleolus 

 lies pressed upon the surface of the nuclear membrane after its extrusion 

 (fig. 9). Also we have observed the contents of the nucleoli to become 

 granular in a few instances. 



The depression, or crater, in the surface of the nuclear membrane 

 appears to last for a considerable time, and gives the appearance of 

 pseudopodial processes when seen in optical section (figs. 4, 7, 8, and 9). 



• " On the Multiplication and Migration of Nucleoli in Nerve Cells of Mammals," by 

 W. Page May and C. E. Walker, this Journal, vol. i.. No. 2, 1908. 



