388 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



also been shown that, as there is no accumulation of these spherules in the nucleus, 

 nor any sign of their absorption, either by the caryolymph or by the chromatin, it 

 is probable, from evidence provided by the nucleus alone, that these spherules 

 pass at once into the cytoplasm. 



Basophile spherules commence to appear in the cytoplasm even before the 

 chromatin has lost its radial relation to the nucleolus, and they occur in increas- 

 ing numbers as growth proceeds until the formation of the definitive yolk nucleus 

 in eggs with a nucleolus of from 7 ij. to 8 ;x in diameter. The spherules are found 

 with all fixing reagents, and are always deeply basophile, even after prolonged 

 extraction. The individual spherules are sharply defined and vary in size from 

 0.5 \L to 1.6 [A, or even occasionally 2 jx. They do not increase in size with the growth 

 of the egg, tlie few spherules first to appear in the young oocyte being as large 

 as the more numerous spherules at later stages, and very small spherules are rare 

 at any stage. The spherules are only occasionally found isolated in the cytoplasm ; 

 far more usually they are associated together in small clusters of from three to 

 six, irregularly disposed around the nucleus and lying either in actual contact with 

 the nuclear membrane or at some little distance from it. They are seldom, how- 

 ever, found far from the nucleus, and are rarely, if ever, found peripheral in 

 position. The spherules of any one cluster vary in size within the limits already 

 noted, and it is rare to find a group consisting solely of very small spherules. 



It has already been noted that, compared with the period intervening between 

 successive discharges, the time actually occupied by the spherules in passing from 

 the nucleolus into the cytoplasm must be very brief, and that this is ample 

 explanation for the rarity with which this process is seen. The few instances 

 in which the passage outward has coincided with the moment of fixation in the 

 still growing oocyte have already been referred to in considering the behavior 

 of the nucleolus. 



In addition to the spatial relation which the nucleolar spherules are frequently 

 seen to bear to those in the cytoplasm, the nucleolar origin of the latter is also 

 indicated by their arrangement in the cytoplasm. It is difficult on any other 

 supposition to account for their arrangement in small groups, irregularly scat- 

 tered around the nucleus; and this arrangement, together with the fact that they 

 are never found in a peripheral position, and that there are, at this stage of the 

 egg's growth, no cells in relation to the egg's periphery, exclude the possibility 

 of an extracellular origin. The fact that the spherules are of much the same 

 size in the youngest as in the older oocytes and that groups of very small spherules 

 are rarely, if ever, seen, exclude both a cytoplasmic origin and a mode of origin 

 by diffusion through the nuclear membrane. 



It should also be noted that the groups in the cytoplasm show no relation 

 to the distal ends of the radially arranged chromatin strands, and moreover 

 continue to appear after this arrangement of the chromatin has been lost. 



The basophile spherules, therefore, which are discharged at intervals in batches 

 from the nucleolus, pass at once into the cytoplasm, and in the young oocyte form 

 scattered groups around the nucleus. 



