302 THE EVOLUTION THEORY 



ovum in every conceivable way, and it is thus stimulated to a growth 

 which no single cell could attain to if it were dependent on the 

 ordinary nutrition supplied by the blood. And we can understand 

 that nature — to speak metaphorically — did not wish to destroy her 

 own work by finally distributing among four ova all the nourishment 

 she had succeeded in heaping up in all sorts of ways within the 

 mother- egg-cell. 



But it may be asked, Why have all these unnecessary divisions 

 been maintained up till the present day ? Why have they not long ago 

 been given up, since they can and do only lead to the production of 

 three abortive ova, which are foredoomed to perish ? Are they mere 

 vestiges, processes which are in themselves meaningless, but have, so 

 to speak, been maintained by the principle of inertia? This principle 

 is certainly operative in some sense and to some extent even in living 

 nature ; a process which has been regularly repeated through a long 

 series of generations does not at once cease to be performed when it 

 is no longer of use to the organism concerned. The eyes of animals 

 which have migrated to lightless depths do not disappear all at once 

 and leave no trace ; they degenerate very gradually and only in the 

 course of many generations ; and it would thus be quite possible to 

 defend the position that these ' polar or maturation divisions ' of the 

 ovum are purely phyletic reminiscences without actual significance. 



But I cannot agree with this opinion. If it were actually so we 

 should expect that the formation of the polar bodies would not still take 

 place in all cases in almost the same manner, for all rudimentary parts 

 and processes vary greatly ; we should expect that in many animal 

 groups the polar divisions would not occur, or perhaps that only half 

 the number would occur. But this is not so ; in all multicellular 

 organisms, from the lowest to the highest, two reducing divisions take 

 place, and always in almost the same manner, with the exception of a 

 single category of ova, of which I shall presently have to speak. We 

 shall see later that even in unicellular organisms analogous processes 

 may be observed. 



But it is also intelligible that this twice repeated division of the 

 mother- egg-cell is necessary if the reduction in the number of 

 chromosomes to half is only possible in this way, since this reduction 

 is indispensable. If each of the two conjugating germ-cells contained 

 the full normal number of chromosomes, the segmentation-nucleus 

 would contain a double number, and if that went on, the number of 

 chromosomes would increase in arithmetical proportion from generation 

 to generation, and would soon become enormous. Even though we 

 were not otherwise certain that these chromosomes are units of a 



