4<J Papers from the Marine Biological Laboratory at Tortugas. 



cause of the loss of chromatin from the spherules. The yellow nucleolus 

 seen after staining with orange G and Lyon's blue must be explained, I be- 

 lieve, on the assumption that here only the plastin element of the nucleolus 

 took a stain, the chromatin element showing no affinity for either of the 

 stains employed. That the nucleolus should select one cytoplasmic (acid) 

 stain and the remainder of the oocyte another, remains inexplicable. Nor 

 does it appear whether the selection is a chemical or a physical phenomenon. 



Chromatin appears to be transported in a highly fluid form through the 

 nuclear reticulum, where some of it becomes condensed as karyosomes, and 

 some carried to the nucleolus, where it is lodged in the form of spherules. 

 Here the chromatin undergoes further elaboration and condensation and is 

 thus imbibed by the plastin, leaving vacuoles more or less emptied of fluid 

 chromatin. Thus the fact that in all living eggs the nucleoli appear vacuo- 

 lated is explained by the reasonable assumption that plastin and fluid chroma- 

 tin in the shape of spherules have different indices of refraction, due to a 

 difference in degree of condensation and possibly of chemical composition. 

 When all the spherules are filled and all the chromatin is approximately at 

 the same stage of elaboration (as at the culmination of the growth-period) 

 the nucleolus stains homogeneously black with iron hematoxylin. When 

 some of the spherules have lost their contained chromatin through extraction 

 by the plastin, real vacuoles appear which seem colored according as the 

 underlying plastin is stained. Whenever the plastin of the nucleolus be- 

 comes freed of the chromatin elements it always stains similar to the linin 

 of the nuclear reticulum. 



Occasionally one finds full-grown oocytes which contain besides one large 

 nucleolus several smaller accessory nucleoli scattered through the nuclear 

 reticulum (fig. 56). I have counted as many as fifty of these in oocytes in 

 which the chief nucleolus was of almost normal size. Most of these were 

 chromatic and stained similar to the chief nucleolus. Evidently such oocytes 

 have a superabundance of chromatin. I have never seen any such oocytes 

 mature. Cases of such eggs observed by me are too rare to permit the gen- 

 eralization that an unusually great amount of chromatin is detrimental to 

 maturation and normal development. There is evidently a slight variation 

 in the amount of chromatin contained in different oocytes of the same 

 individual, but a limit is probably reached beyond which a greater amount 

 is abnormal. These cases, however, give certain evidence that the chromatin 

 may manufacture plastin, or at least compel the morphological arrangement 

 and chemical modification of plastin (linin) to be used as ground-substance, 

 for it was frequently possible to see that these accessory nucleoli had each a 

 plastin ground-substance, and occasionally one was seen with vacuoles similar 

 to those of the chief nucleolus. Again, when the female pronucleus is 

 formed it always contains a plastin nucleolus (plasmosome) (figs. 82, 83, 

 84). Very rarely this was seen to be chromatic (fig. 81), which may mean 



