21 8 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



greatly preponderate in the young egg-cell, for, as we have 

 already seen, it controls the growth of the latter. The germ- 

 plasm, on the other hand, can only be present in minute 

 quantity at first, but it must undergo considerable increase 

 during the growth of the cell. But in order that the germ- 

 plasm may control the cell-body, or, in other words, in order 

 that embryonic development may begin, the still preponder- 

 ating ovogenetic nucleoplasm must be removed from the cell. 

 This removal takes place in the same manner as that in which 

 differing nuclear substances are separated during the ontogeny 

 of the embryo : viz. by nuclear division, leading to cell-division. 

 The expulsion of the polar bodies is nothing more than the 

 removal of ovogenetic nucleoplasm from the egg-cell. That 

 the ovogenetic nucleoplasm continues to greatly preponderate 

 in the nucleus up to the very last, may be concluded from the 

 fact that two successive divisions of the latter and the expul- 

 sion of two polar bodies appear to be the rule. If in this way 

 a small part of the cell-body is expelled from the ^gg, the ex- 

 trusion must in all probability be considered as an inevitable 

 loss, without which the removal of the ovogenetic nucleoplasm 

 cannot be effected. 



This is my theory of the significance of polar bodies, and 

 I do not intend to contrast it, in extenso, with the theories pro- 

 pounded by others ; for such theories are well known and 

 differ essentially from my own. All writers agree in supposing 

 that something which would be an obstacle to embryonic de- 

 velopment is removed from the egg ; but opinions differ as to 

 the nature of this substance and the precise reasons for its 

 removal ^ Some observers (e.g. Minot '\ van Beneden, and 

 Balfour) regard the nucleus as hermaphrodite, and assume 

 that in the polar bodies the male element is expelled in order 

 to render the egg capable of fertilization. Others speak of 

 a rejuvenescence of the nucleus, others again believe that the 



^ Thus in 1877 Biitschli thought that ' the chief significance of the 

 formation of polar bodies Hes in the removal of part of the nucleus of the 

 egg, whether this removal is effected by simple expulsion or by the 

 budding of the egg-cell.' ' Entw^icklungsgeschichtliche Beitrage ; ' 

 Zeitschrift fiir wissenschaftliche Zoologie, Bd. XXIX. p. 237, foot- 

 note. 



- C. S. Minot, 'Account,' etc.; Proc. Boston Soc. Nat. Hist. vol. xix. 

 p. 165, 1877. 



