Fig. 23. Two successive stages in the gradual metamorphosis of the germinal vesicle and spot of the ovum of Asterias glacialis immediately after it is laid (copied from Fol).
The germinal spot at the same time loses its clearness of outline and gradually disappears from view.
At this stage, and between it and the stage represented in [fig. 26], the action of reagents brings to light certain appearances the nature of which is not yet fully cleared up for Asterias, which have been described somewhat differently by Fol for Ast. glacialis and Hertwig for Asteracanthion.
Fig. 24. Ovum of Asterias glacialis shewing the clear spaces in the place of the germinal vesicle. Fresh preparation (copied from Fol).
Fol finds immediately after the stage just described that a star is visible between the remains of the germinal vesicle and the surface of the egg, which is connected with an imperfectly-formed nuclear spindle extending towards the germinal vesicle[28]. At the end of the nuclear spindle may be seen the broken up fragments of the germinal spot.
At a slightly later stage, in the place of the original germinal vesicle there may be observed in the fresh ovum two clear spaces ([fig. 24]), one ovoid and nearer the surface, and the second more irregular in form and situated rather deeper in the vitellus. In the upper space parallel striæ may be observed. By treatment with reagents the first clear space is found to be formed of a horizontally-placed spindle with two terminal stars, near which irregular remains of the germinal spot may be seen. Slightly later ([fig. 25]) there may be seen on the lower side of the spindle a somewhat irregular body, which may possibly be part of the remains of the germinal spot, though Fol holds that it is probably part of the membrane of the germinal vesicle. The lower clear space visible in the fresh ovum now contains a round body, [fig. 25]. Fol concludes that the spindle is formed out of part of the germinal vesicle and not from the germinal spot, while he sees in the round body present in the lower of the two clear spaces the metamorphosed germinal spot. He will not, however, assert that no fragment of the germinal spot enters into the formation of the spindle.
