228 BULLETIN OF THE 



found at a somewhat later period ; at a time, namely, when the spindle 

 of the first cleavage sphere is fully formed (Figs. 88, 89), and possessed 

 of equatorial thickenings. 



The remnants of the nuclear structure sustain such a topographical 

 relation to the forming amphiaster and spindle as to leave little doubt 

 that the latter take their origin nearer the centre of the vitellus than 

 the place occupied by the pronuclei, so that the substance of the pro- 

 nuclear bodies moves from its superficial position toward the centre in 

 contributing to the formation of the spindle. The opinion that such a 

 motion of nuclear substance as here suggested actually takes place, may 

 find support in the shape often presented by this nuclear remnant. It 

 seems to be elongated toward the amphiaster, and sometimes shows 

 (Fig. 87) a sort of filamentous structure, as though individual fibres of 

 substance were being drawn into the forming spindle. These nuclear 

 remnants are flattened in such a manner that they are seen edgewise 

 when one looks along the axis of the forming spindle. As a conse- 

 quence, they are more conspicuous when viewed in this position than 

 when seen en face. In the latter case the outline is much less regular, 

 and in places may be quite indistinguishable ; especially is this the case 

 along the border directed toward the amphiaster. For this reason it 

 is not easy to satisfy one's self as to the exact direction in which the 

 nuclear substance is tending. Seen edgewise, it is unequivocally directed 

 toward the axis of the spindle. But toward which part of the axis, — 

 toward the middle, or toward one or both of its apices'? This can be 

 satisfactorily answered only by a study of the face view. Though not 

 so satisfactory as the former aspect, this view favors the belief that the 

 nuclear substance is being transferred toward the equatorial region of 

 the spindle. 



The spindle is formed some time after the first appearance of the 

 stellate figures. It is only in an advanced stage of the metamorphosis 

 that the existence of such a structure, distinct from the general radia- 

 tion about the centres of the two asters, becomes evident. I have 

 seen very delicate and inconspicuous fibres stretching from star to 

 star outside the pronuclear structures at the early stage represented 

 in Fig. 85. These, however, are not distinguishable from the neigh- 

 boring rays of the asters, unless it be by a somewhat greater length. 

 The centres of the stars lie deeper (farther from the animal pole) 

 than the adjacent surfaces of the pronuclei, so that if spindle fibres 

 are present, as I believe, they must lie external to the pronuclei. 

 Even in the later stage represented by Fig. 82 the limits of the spindle 



