Henry Gray (18251861). Anatomy of the Human Body. 1918.
Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In I the polar spindle (sp) has advanced to the surface of the egg. In II a small elevation (pb1) is formed which receives half of the spindle. In III the elevation is constricted off, forming the first polar body (pb1), and a second spindle is formed. In IV is seen a second elevation which in V has been constricted off as the second polar body (pb2). Out of the remainder of the spindle (f.pn in VI) the female pronucleus is developed.