212 BULLETIN OF THE 



its of discernment with Hartnack, obj. 7, oc. 4. These contained bodies 

 or nucleoli, are very strongly refractive, and consequently appear as 

 brilliant and conspicuous objects within the pronucleus, especially when 

 treated with osmic acid followed by carmine staining. They are not 

 always evenly distributed through the pronucleus, but are often grouped 

 in different parts of its substance. No considerable portion of the pro- 

 nucleus, however, is destitute of nucleoli. 



The extent to which the inner star of the second archiamphiaster con- 

 tinues to hold sway in the vitellus is subject to variation. Often it is 

 seen still at its maximum after the female pronucleus has acquired a 

 diameter of 15 /t or 20 fx. At other times it is much less extensive 

 (Fig. 63), even at the beginning of the formation of the pronucleus. 

 The latter unquestionably continues to increase in size, and sometimes 

 retreats a little from the animal pole of the yolk toward its centre ; more 

 often, I believe, it remains quite near the surface, — at the place it oc- 

 cupied when the confluence of the thickenings began. 



Simultaneously with its increase in dimensions occurs an increase in the 

 number of nucleoli. How the new nucleoli arise — whether by division 

 of those previously existing or not — must, in default of direct obser- 

 vations, remain undetermined ; yet the entire absence of forms showing 

 any of the stages of division affords no support to the supposition of 

 such an origin. There are, it is true, some deviations from this relation 

 between the increase in the size of the nucleus and the increase in the 

 number of nucleoli (Figs. 70, 77) ; but, in general, I think the cor- 

 rectness of the statement cannot be doubted. It is also quite certain 

 that the size of the larger nucleoli is directly proportional to the size of 

 the pronuclei themselves ; so that a growth concomitant to that of the 

 pronucleus may fairly be assumed. The nucleoli appear perfectly homo- 

 geneous, and very prominent in osmic acid preparations; in acetic acid, 

 on the other hand, they are less distinct, and on the average somewhat 

 larger. The outline, even with the latter method of treatment, remains 

 full and entire, and in some cases it appears double ; but nothing like 

 a double contour is seen in preparations with osmic acid. Neither 

 vacuoles, nor granulations, nor punctations, are discernible within the 

 nucleoli by any method of treatment employed. 



The changes which further affect the female pronucleus are rather 

 those of growth than of migration. It is especially significant that 

 this female pronucleus remains constantly near the surface of the vitel- 

 lus. However much it may increase in diameter, its removal from the 

 animal pole is never great, in most cases altogether inappreciable. 



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