384 BULLETIN OF THE 



of its formation. I see it in shape substantially as Strasburger has 

 figured it {loc. cit, Taf. VII. Fig. 21, and Taf. VIII. Figs. 9, 12), —a 

 pear-shaped body with its blunter end directed toward the plane of seg- 

 mentation (Limax, Fig. 80^), but in position it is quite different. The 

 more pointed end does not correspond to the centre of attraction (" Pol ") 

 as he represents it, but is removed from the " Pol " half the long diam- 

 eter of the nucleus at a time when several nucleoli have made their 

 appearance. This distance makes the more certain the conclusion of 

 Strasburger, that the " Pol " furnishes no " Formelemente " to the grow- 

 ing nucleus, and has suggested the possibility that this central portion 

 of the " area " might not be nuclear substance, and that it might not 

 enter into the composition of the new nucleus, but become finally dif- 

 fused in the protoplasm of the yolk. 



The differentiation of the nucleus into more and less dense portions is 

 not so clearly localized as in Strasburger's Fig. 21, Taf. VIL, although 

 the nucleoli are here (Fig. 80^) more abundant at the blunt end. The 

 peculiar /orm I would explain as brought about by the continued attrac- 

 tion of the so-called Polsubstanz upon the nucleus combined with the 

 increasing opposition offered to its actual progression by the increasing 

 density^ of the protoplasm nearer the centre of the '' area." * The sub- 

 sequent assumption of a more nearly spherical form would then be but 

 the natural result of a gradual diminution of the attractive force, further 

 evidence of which is seen in the gradually fading rays of the protoplas- 

 mic aster. Strasburger is " convinced that the form of the cell nucleus 

 is to be taken as the expression of the forces operating in its interior." 

 With that conception the peculiar pear-shaped form now under consider- 

 ation could not easily be otherwise explained than as I have suggested 

 in the foot-note, for the " Polsubstanz " most certainly at this time forms 

 no part of the interior of the nucleus. A corresponding relationship of 

 " centre of attraction " and nuclear bodies is shown for the pronuclei of 

 Limax in Fig. 68. This seems to me a confirmation of the view which 

 makes the peculiar form due to the attractive influence of substance 

 which lies outside both the pronuclei, and which also induces a stellar 

 figure in the surrounding protoplasm. 



The most serious obstacle to the view which I have suggested is found 

 in the formation of free nuclei, where, to make use of Strasburger's 



* In view, however, of the automatic form-changes of which the nucleus is cer- 

 tainly at times capable, it may not be erroneous to look upon this pointed extremity 

 as a sort of pseudopodal prolongation, having an important function in the nutrition 

 of the nucleus from the substance of the "area." 



