186 BULLETIN OF THE 



not always the stouter lines, however, which are traceable farthest from 

 the centre. 



The diameter of each of these sun-like or astral spheres is about one 

 third that of the whole vitellus, and their centres are so situated as to 

 divide the diameter of the yolk into three nearly equal portions, so that 

 the two astral spheres appear at first sight to be simply tangent to each 

 other. A more careful examination shows that this region of contact 

 presents important, though not prominent, modifications of structure. 

 All the fibres for some distance around the point of tangency are contin- 

 uous from one sphere to the other. The stout fibres are here compara- 

 tively more numerous than in the other portions of the figure, and all 

 are more or less curved ; those farthest from the central point of con- 

 tact are most curved. This bipolar mass constitutes a spindle-shaped 

 body, having its apices at the centres of the two spheres. It is the 

 " Richtungsspindel " of German writers. I shall call it the " maturation 

 spindle." The fibres which help to form it differ so little from the radial 

 filaments of the suns that it is difficult at first to distinguish between the 

 two. There is, however, still a third peculiarity which helps to empha- 

 size this difference. The fibres of the spindle are slightly thickened 

 midway between the two poles. These thickenings form the nuclear 

 plate (Kernplatte) of Strasburger. From the results of recent obser- 

 vations made on more favorable objects by numerous European ob- 

 servers, there is every reason to believe that this spindle-shaped body 

 is the result of the direct metamorphosis of the germinative vesicle, or 

 at least of a part of it. A careful examination, however, of all the early 

 stages I have seen, has failed to show satisfactorily anything of the 

 germinative vesicle, which a somewhat earlier stage would probably have 

 disclosed.* I cannot avoid repeating the fact that, at this stage, the 

 spindle fibres are very inconspicuously diff'erentiated from the radial fila- 

 ments. Except for much more satisfactory views at a later stage, I 

 confess I should have been somewhat sceptical about the existence of 

 such a structure distinct from the stellate figures. 



It will be noticed that already the vitellus has no longer an homaxial 

 form, but is monaxial. The differentiated axis corresponds to that of 

 the maturation spindle ; and its two poles are, so far as I have been 

 able to discover, absolutely alike (haplopolar condition). This state 



* In one case (Fig. 39) I saw near the plane of the nuclear plate outside the spindle 

 a few irregularly shaped bodies considerably larger than the granulations surrounding 

 them, which may possibly have been remnants of the germinative dot, or of the mem- 

 brane of the germinative vesicle. If not the remains of nuclear substance, I know 

 of nothing with which they might be compared. 



J 



