MATURATION AND IMPREGNATION OF THE OVUM. 



119 



The spindle, however it be formed, has up to this time been 

 situated with its axis parallel to the surface of the egg, but 

 not long after the stage last described a spindle is found with one 

 end projecting into a protoplasmic prominence which makes its 

 appearance on the surface of the egg (Fig. 6). Hertwig believes 

 that the spindle simply travels towards the surface, and while 

 doing so changes the direction of its axis. Fol finds, how- 

 ever, that this is not the case, but that between the two conditions 

 of the spindle an intermediate one is found in which a spindle 

 can no longer be seen in the egg, but its place is taken by a com- 

 pact rounded body. He has not been able to arrive at a conclu- 

 sion as to what meaning is to be attached to this occurrence. In 

 any case the spindle which projects into the prominence on the 



Tig. 7. — Portion of the ovum of Asterias glacialis at the moment of the 

 detachment of the first polar body and the withdrawal of the remain- 

 ing part of the spindle within the ovum. Picric acid preparation 

 (copied from Fol ). 



surface of the egg divides it into two parts, one in the prominence 

 and one in the egg (Fig. 7) . The prominence itself with the 

 enclosed portion of the spindle becomes partially constricted off 



Pig. 8.— Portion of the ovum of Asterias glacialis, with the first polar 

 body as it appears when living (copied from Pol.). 



Pig. 9. — Portion of the ovum of Asterias glacialis immediately after the 

 formation of the second polar body. Picric acid preparation (copied 

 from Pol.). 



