162 THE EVOLUTION OF SEX. 



continuity of heredity, by passing intact into the reproductive cells of the 

 next generation. Besides this all-important " germ-plasma," the nucleus 

 of the ovum contains, according to Weismann, an " ovogenetic nuclear 

 plasma," which is of no direct importance in development, but is useful to 

 the ovum simply as an ovum. It is the substance which is supposed to 

 have to do with the general upbuilding of the egg-cell, with the accumu- 

 lation of yolk, secreting of membranes, and the like. 



" The first polar body implies the removal of the ovogenetic nuclear 

 plasma, which has become superfluous when the egg has attained maturity. 

 The second polar body, on the other hand, implies the removal of a portion 

 of the germ-plasma itself. This is so effected that the number of ancestral 

 elements {Ahnen-idioplasmen) which compose it is reduced to a half. A 

 similar reduction must also take place in the number of the male germ- 

 elements. 



" Parthenogenesis occurs when the entire sum of the ancestral elements 

 persists in the nucleus of the ovum. Development by fertilisation demands, 

 however, that half of these ancestral elements m.ust first be extruded from 

 the ovum, whereupon the remaining half, in uniting with the sperm nucleus, 

 regains the original number. 



" In both cases the beginning of development depends upon the presence 

 of a definite, and indeed similar mass of germ-plasma. In the ovum which 

 requires ferlilisation, this is afforded by the importation of the sperm-nucleus, 

 and development follows on the heels of fertilisation. The parthenogenetic 

 ovum already contains the necessary mass of germ-plasma, and this becomes 

 active as soon as the single polar body has freed the ovum from the ovo- 

 genetic nuclear-plasma." 



Now if it be true that a constant difference between an egg which can 

 develop of itself and one that cannot, is that the former extrudes one tiny 

 cell, and the latter, so far as yet observed, two, Weismann must be right in 

 emphasising that part at least of the secret of parthenogenesis lies here. 

 Partly hidden still, however, if one dare ask what there is about the par- 

 thenogenetic ovum which limits its primitive budding to once instead of 

 twice. Not altogether so subversive of Minot's theory either, as Weismann 

 would make out. Minot, as we saw, accepts ihe facts, but ingeniously 

 supposes that the polar element retained in parthenogenetic ova is a male 

 element. It is necessar)', however, to examine Weismann's theory more 

 closely, not only in its direct relation to the problem of parthenogenesis, 

 but because of its postulates, which run so directly counter to our reading 

 of the phenomena of sex. 



(i.) Weismann's theory obviously differs very emphatically from those 

 previously suggested. The first polar body is no skimming of antagonistic 

 male material ; the very reverse, it is an extrusion of ovogenetic nuclear 

 material which had to do with the upbuilding of the ovum, an emphatically 

 female function. Nor is the second polar extrusion in any way an expulsion 

 of male elements ; it is a giving away of some of the precious germ-plasma, 

 the bearer of hereditary characteristics. Furthermore, even the sperm 

 nucleus is in no peculiar sense male material ; it might as well be another 

 ovum-nucleus. It has only a quantitative value, to restore to the nucleus 

 of the ovum an amount of germ-plasma equivalent to that which has been 

 so recklessly squandered. 



(2.) But Weismann's theory, based on the observation of facts, is in 

 itself full of hypotheses. This distinction between ovogenetic and germ- 



