The answer to the first of these questions is not difficult to find. The formation of the polar bodies is independent of impregnation, and is the final act of the normal growth of the ovum. In a few types the polar cells are formed while the ovum is still in the ovary, as, for instance, in some species of Echini, Hydra, etc., but, according to our present knowledge, far more usually after the ovum has been laid. In some instances the budding-off of the polar cells precedes, and in other instances follows impregnation; but there is no evidence to shew that in the latter cases the process is influenced by the contact with the male element. In Asterias, as has been shewn by O. Hertwig and Fol, the formation of the polar cells may indifferently either precede or follow impregnation--a fact which affords a clear demonstration of the independence of the two occurrences. To the second of the two questions it does not unfortunately seem possible at present to give an answer which can be regarded as satisfactory. The retrogressive changes in the membrane of the germinal vesicle which usher in the formation of the polar bodies may very probably be viewed as a prelude to a renewed activity of the contents of the vesicle; and are perhaps rendered the more necessary from the thickness of the membrane which results from a protracted period of passive growth. This suggestion does not, however, help us to explain the formation of polar bodies by a process identical with cell division. The ejection of part of the germinal vesicle in the formation of the polar cells may probably be paralleled by the ejection of part or the whole of the original nucleus which, if we may trust the beautiful researches of Bütschli, takes place during conjugation in Infusoria as a preliminary to the formation of a fresh nucleus. This comparison is due to Bütschli, and according to it the formation of the polar bodies would have to be regarded as assisting, in some as yet unknown way, the process of regeneration of the germinal vesicle. Views analogous to this are held by Strasburger and Hertwig, who regard the formation of the polar bodies in the light of a process of excretion or removal of useless material. Such hypotheses do not, unfortunately, carry us very far. I would suggest that in the formation of the polar cells part of the constituents of the germinal vesicle, which are requisite for its functions as a complete and independent nucleus, is removed, to make room for the supply of the necessary parts to it again by the spermatic nucleus.