Several of Hertwig's figures closely correspond with those of Fol, and considering how conflicting is the evidence before us, it seems necessary to leave open for Asterias the question as to what parts of the germinal vesicle are concerned in forming the first spindle. A clearer view of the phenomena which take place at this stage has been obtained by Fol in the case of Heteropods (Pterotrachæa). In the ovum a few minutes after it has been laid the germinal vesicle becomes very pale, and two stars make their appearance round a clear substance near its poles. The nucleus itself is somewhat elongated, and commences to exhibit at its poles longitudinal striæ, which gradually extend towards the centre at the expense of the nuclear reticulum, from a metamorphosis of which they are directly derived. When the striæ of the two sides have nearly met, thickenings may be observed in the recticulum between them, which give rise, where the striæ of the two sides unite, to the central thickenings of the fibres (nuclear plate). In this way a complete nuclear spindle is established[29]. [29] For the further details on the nuclear spindle _vide_ the next Chapter. The important result of Fol's observations on Heteropods, which tallies also with what is found in Asterias, is that a spindle with two stars at its poles is formed from the metamorphosis of the germinal vesicle and surrounding protoplasm (fig. 25). [FIG. 26. PORTION OF THE OVUM OF ASTERIAS GLACIALIS AT THE MOMENT OF THE DETACHMENT OF THE FIRST POLAR BODY AND THE WITHDRAWAL OF THE REMAINING PART OF THE SPINDLE WITHIN THE OVUM. PICRIC ACID PREPARATION (copied from Fol).] Polar cells. The spindle has up to this time been situated with its axis parallel to the surface of the egg, but in somewhat older specimens a vertical spindle is found, with one end projecting into a protoplasmic prominence which makes its appearance on the surface of the egg (fig. 26). Hertwig believes that the spindle simply travels towards the surface, and while doing so changes the direction of its axis. Fol asserts, however, that this is not the case, but that between the two phases 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 body with a dentated outline. He has not been able to arrive at a conclusion as to what meaning is to be attached to this occurrence, which does not appear to take place in Heteropods. [FIG. 27. PORTION OF THE OVUM OF ASTERIAS GLACIALIS, WITH THE FIRST POLAR CELL AS IT APPEARS WHEN LIVING (copied from Fol).]