Fig. 27. Portion of the ovum of Asterias glacialis, with the first polar cell as it appears when living (copied from Fol).
In any case the spindle which projects into the prominence on the surface of the egg divides into two parts, one in the prominence and one in the egg ([fig. 26]). The prominence itself with the enclosed portion of the spindle becomes constricted off from the egg to form a body, well known to embryologists as the polar body or cell ([fig. 27]). Since more than one polar cell is formed, that which is the earliest to appear may be called the first polar cell.
Fig. 28. Portion of the ovum of Asterias glacialis immediately after the formation of the second polar cell. Picric acid preparation (copied from Fol).
The part of the spindle which remains in the egg becomes directly converted into a second spindle by the elongation of its fibres, without passing through a typical nuclear condition. A second polar cell next becomes formed in the same manner as the first ([fig. 28]), and the portion of the spindle remaining in the egg becomes converted into two or three clear vesicles ([fig. 29]), which soon unite to form a single nucleus ([fig. 30]). The new nucleus which is clearly derived from part of the original germinal vesicle is called the female pronucleus, for reasons which will appear in the sequel.
Fig. 29. Portion of the ovum of Asterias glacialis after the formation of the second polar cell, shewing the part of the spindle remaining in the ovum becoming converted into two clear vesicles. Picric acid preparation (copied from Fol).