Kntliarine Foot and E. C. Strobell 207 



show that nianv of tlie vacuoles contain a substance which after some fixa- 

 tives can be so densch' stained that the entire nucleohis appears homogen- 

 eous, these results su})portino- the observations of investigators who claim 

 that the so-called vacuoles of the nucleolus contain a fluid substance. In 

 dried germinal vesicles we have not been able to demonstrate any vacuoles 

 in the nucleolus, but in the living egg we have sometimes seen a single 

 vacuole in the principal nucleolus. In one case the nucleolus at first 

 showed no vacuole, one app(>aring about five minutes after the egg was 

 under observation and persisting until the egg died. In other eggs the 

 large nucleolus at first contained a vacuole which disappeared in about 

 five minutes, this condition persisting until the egg died. It Avould 

 seem, therefore, that vacuoles in the principal nucleolus of living eggs 

 appear and disappear as maintained by some authors. 



3Iany of ]Montgomery's figures sliow the vacuole stained in differential 

 colors, but his interpretation that they " are derived from the small 

 fluid globules which flrst appear in the .nuclear sap " is not supported by 

 Allolohophora. Photo. 57, Plate III, might be forced to such an inter- 

 pretation, but in the light of more than fifty other negative examples 

 it must be interpreted with them as merely another expression of the 

 effect of fixation and dehydration on the more fluid portion of the 

 nucleolus. Even unstained preparations show that the refractive parts 

 of the principal nucleolus and its vaciioles represent two substances of 

 very different degrees of density and this must produce an unstable 

 condition which is very readily disturbed by fixatives, and must be, 

 therefore, largely responsible for the great variety of forms seen in fixed 

 material. 



The vacuoles in the principal nucleolus of Allolohopliora sometimes 

 appear to be true vacuoles and again they appear to be a thin fluid sub- 

 stance which can be stained so as to completely obliterate the vacuoles 

 (see Photos. 22 and 27, Plate II), which will reappear after decoloring 

 as shown in Photos. 37, 42, Plate II, 49, 53, 54, 58, 60, Plate III, etc., 

 and again the contents of many ring-like nucleoli closely resemble 

 the surrounding nucleoplasm suggesting that it has been artificially 

 forced into the nucleolus. This condition is shown in Photos. 36, 38, 

 43, 44, 45, Plate II, 50, Plate III, 79, Plate IV, 93, 94, 95, 96, and 98b, 

 Plate Y, and many of these resemble the nucleoli figured by Coe, '99, in 

 Cerehratulus. In some cases, e. g., Photo. 50, Plate III, it is clearly seen 

 that a substance is massed in the nucleolus at the expense of the surround- 

 ing nucleoplasm, and Photo. 9Sa and b, Plate V, show a distinct break in 

 the nucleolar ring indicating how the fluid portions of the nucleolus and 

 the nucleoplasm may be brought into contact. Many nucleoli which are 



