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nuclear membrane. The nuclear membrane is often seen to protrude con- 

 siderably at this point (fig. 11), and then the nucleolus passes through into 

 the cytoplasm (figs. 12 and 13). Sometimes this protrusion is very large 

 compared with the size of the nucleolus, and then it seems to be depressed in 

 the middle in a form not unlike the crater of an extinct volcano, the nucleolus 

 lying at the bottom of the crater. When seen under the microscope, this 

 formation gives the appearance of two protrusions, one on either side of 

 the nucleolus. This is due to the fact that the crater formation is seen in 

 actual or in optical section. The nuclear membrane is re-formed very quickly, 

 and is, as far as can be ascertained, always re-formed long before the 

 nucleolus leaves the outer surface of the nuclear membrane. That the 

 nucleoli remain contiguous to the nuclear membrane for some time is 

 rendered highly probable, if not actually certain, by the fact that in every 

 slide examined a very large number were seen in this position. That the 

 passage of the nucleolus is brief, is rendered probable by the fact that 

 nucleoli in the act of passing through are very rarely to be found in 

 comparison with those in any other position either inside or outside the 

 nucleus. That the nuclear membrane is re-formed before the nucleolus 

 leaves its outer surface is rendered almost certain by the fact that nucleoli 

 are comparatively frequently found lying adjacent to or upon it, but no 

 breach in the neighbourhood was ever observed. In the latter case, the 

 surface of the nucleolus that is touching the nuclear membrane being con- 

 cave, a comparatively large area of membrane is covered by it (figs. 14 

 and 15). Whether the extruded nucleolus always remains thus attached 

 to the membrane, however, appears doubtful, as it has been found in this 

 position comparatively seldom. More often it is found adjacent to the 

 nucleus, but not compressed upon its membrane (fig. 16). No breach in 

 the nuclear membrane has been found that could legitimately be connected 

 with the passage of a nucleolus at any other time than during the actual 

 process of passing through. 



The nucleoli that migrate appear to be usually, if not always, among 

 the largest found in the nuclei of the nerve cells. After they have passed 

 into the cytoplasm they increase in size, often to a considerable extent, and 

 the contents seem generally to become definitely granular. 



One of the most remarkable facts in connection with this migration of 

 the nucleoli is that as they pass into the cytoplasm their staining 

 reaction alters. Thus with Method A the nucleoli inside the nucleus 

 are blue or violet. Those passing through are purple or red. Those definitely 

 outside are bright red or pink, and those which have travelled away from 

 the nuclear membrane are pink or red. With Method B the nucleoli inside 

 the nucleus are brilliant scarlet. Those passing through are reddish orange, 

 and those which have passed through a pale orange or yellow. Nucleoli 

 that have been artificially forced out of the nucleus by the knife of the 

 microtome stain exactly as do those that are found in the nuclei. This 

 suggests strongly that some important chemical or physical change 



