140 ORIGIN OF YOLK IN OVA OF AX ENDOPARASITIC COPEPOD, 



phibia, the peripheral nucleoli generate a substance which diffuses 

 first into the nucleus, and from there into the cytoplasm; finally, 

 it combines with the cytoplasm to form yolk. Henneguy(2) be- 

 lieves that the corpuscles of Balbiani in vertebrates are either 

 parts of the nucleolus, or the entire nucleolus, which pass through 

 the nuclear wall into the cytoplasm. Montgomery (6), in Pisicola, 

 describes the nucleus as contracting in volume, and, in so doing, 

 discharging all except one of its nucleoli into the cytoplasm. 

 Goldschmidt(l), in active gland-cells and in muscle-cells of Ascaris, 

 has described a cytoplasmic chi'omatin, which, instead of being- 

 gathered into irregular masses as in the Kissl bodies of nerve- 

 cells, is arranged in fibres or coarse reticula. In most instances, 

 however, this chromatin, which he calls 'Chromidialapparat,' is 

 not derived from nucleolar material, but represents nuclear chro- 

 matin which has made its way into the cytoplasm. In fact, in 

 many cases, the chromatin-fibres of the cytoplasm extend directl}' 

 through the nuclear membrane, and are continuous with the 

 chromatic reticulum of the nucleus. Since the chromatic appa- 

 ratus is more highly developed in active than in resting cells, 

 Goldschmidt concludes that it umst function in the metabolism 

 of the cytoplasm. 



My own deductions may now be put very briefly. They are : — 



1. The yolk-granules are formed by the combination of a cyto- 

 plasmic constituent with chromatin. 



2. The first yolk-granules are formed within the nucleus. 



3. The formation of the new nucleus is a pseudo-contraction of 

 the overladen, old nucleus. 



4. This pseudo-contraction leads to the shedding of some of the 

 karyosomes, which are henceforward to be regarded as yolk-nuclei. 



5. These yolk-nuclei are stores of chromatin, which are to con- 

 tinue the functional activity of the nucleus of the growing pri- 

 mary oocyte, that is to say, they are to supply chromatin for 

 that combination which is yolk-formation. 



6. The ultimate oogonium is nourished by endosmosis, the 

 primary oocyte by the epithelium of the oviduct. In both cases, 

 the all-important substance recei\ ed is the cytoplasmic constituent 



