580 BULLETIN OF THE 



on the contrary, to be assured of the absence of every connective filament in 

 this region ; it is occupied by a uniformly granular vitellus. Since acetic 

 acid has the effect of making all sarcodic filaments so distinct, this fact appears 

 to the author significant [of what ?]. I think no difficulty can be experienced 

 in interpreting Fig. 9 ; it is Fig. 1 1 which still remains to be explained. I be- 

 lieve it corresponds to my Fig. 82. That the latter does not exhibit a stage 

 subsequent to the formation of the equatorial plate is evident from a comparison 

 with Figs. 90-93. I have assumed that it corresponds to a stage preceding the 

 formation of a veritable spindle. The principal difficulty with this, as with 

 Fol's interpretation, is in explaining what has become of the substance which 

 usually appears at this time in the form of spindle-fibre thickenings. To 

 assume, as Fol does, that this substance has already passed through the stages 

 of division and migration, is in contradiction with every other figure he has 

 given. I am not sure that both these cases may not represent abnormal condi- 

 tions, — either a more complete dissolution and distribution of the substance 

 of the nucleus than is usual, or a failure of the vitellus to respond as promptly 

 as usual to the changes in the nucleus. It is perhaps possible that Fol's Fig. 11 

 represents a stage nearly corresponding with that of his Fig. 14 (PI. VII.), and 

 that the envelope of the nucleus has simply disappeared a little sooner than 

 usual. Ill that event, there might be some reason, even in his observations, 

 for retaining the view that the spindle fibres are at first composed of vitelline 

 filaments. But however that may be, further observations are necessary to 

 render either of these figures (Fig. 11 or Fig. 82) satisfactorily intelligible. 



During the next stage the constriction of the yolk begins, and the second 

 membrane is detached on all sides, although it follows the constriction for a 

 certain distance. The " grains de Biitschli " reach the sarcodic mass of their 

 respective asters, at the edge of which they appear as small spherical bodies, 

 sometimes still arranged in a plane parallel to the equator, sometimes without 

 order. They vary in size and are hollow. At the opposite margin of each 

 " area " is another group of much smaller globules. The latter are still abun- 

 dant, and derived in all probability from the central granular masses of the 

 asters. Ultimately these two groups are intermingled. This may take place 

 before the larger globules have become hollow, or not till after they have in 

 addition each acquired a nucleolus. 



The stage which follows ends with the separation of the segmentation spheres. 

 The asters continue to move apart and pass the centres of their respective 

 spheres ; the "areas" have become conical or pyriform. The rays are curved, 

 as already described by Auerbach. The vitelline membrane has failed to fol- 

 low the furrow, and stretches across it from one sphere to the other. In picric 

 acid the larger globules of the " area " are increased in size, and each contains a 

 nucleolus. They are, therefore, true nuclei. The larger they (nuclei) are, the 

 less their number, from which it is probable that they unite with each other. 

 Their arrangement is irregular. The rays on the outer side of the "area" 

 converge toward a point at the external side of the mass ; all the other rays, 

 toward the centre of the mass. In osniic acid the exterior form of the yolk 



a 



