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BULLETIN 82, UNITED STATES NATIONAL. MUSEUM. 



food material of the chromatin, which thus, unlike that of the nucleolus, shows so 

 little relation to the requirements of particular cell structures, is the nutritive and 

 oxygenated plasma of the parent organism which enters the tissues of the ovary 

 from the surrounding sinus. In this connection the invariably superficial position 

 in the ovary of the growing oocyte at the time when this activity of the chromatin 

 is at its maximum should be noted. 



Professor Chubb has already given reasons for assuming the passage of sub- 

 stance from the chromatin to the nucleolus; he believes there is also evidence for 

 assuming the passage of substance from the chromatin to the cytoplasm. During 

 the early growth of the oocyte, prior to yolk formation, the cytoplasm is not only 

 increasing in quantity but is also steadily accumulating material to be subsequently 

 utilized in yolk formation, this accumulation being indicated by the progressively 

 increasing basophile reaction of the cytoplasm. During this period the chromatin, 

 from being massed around the nucleolus, has become finely subdivided, and has, at 

 the same time, lost much of its affinity for the basic stain. With the commencement 

 of yolk formation, on the other hand, the chromatin shows a progressively increas- 

 ing staining capacity, and at the same time deeply staining droplets appear on the 

 threads and gradually increase in number and size. Professor Chubb interprets 

 the faintly stained condition of the chromatin prior to the commencement of yolk 

 formation as due to the avidity with which the cytoplasm at this stage takes up the 

 products of the chromatin activity. The cai\yolyrnph is thus always unsaturated and 

 absorbs this material as fast as the chromatin can produce it. With the commence- 

 ment of the probably automatic changes in the cytoplasm by which this accumulated 

 material is converted into the definitive yolk spherules, there is, as we should 

 expect, a marked diminution in the avidity with which the cytoplasm absorbs the 

 products of chromatin activity. The chromatin, however, continues, for a time at 

 least, to produce them in as great a quantity as before, but the caryolymph, being 

 now saturated, no longer removes them, and they therefore slowly accumulate on 

 the chromatin threads, causing both the deeper staining of the latter and the forma- 

 tion of the chromatin spherules. 



Up to the commencement of yolk formation the nucleus, like the nucleolus, in- 

 creases steadily in size step by step with the growth of the cytoplasm, the ratio of 

 their diameters remaining almost, if not quite, constant. Thus the nucleus is 

 usually a little over a half, the nucleolus a little under a quarter, the diameter of 

 the egg. The following measurements show this relation at different periods of the 

 egg's growth prior to yolk formation, the figure given for each stage being the mean 

 of a considerable number of closely approximating measurements : 



