VI.] THEIR SIGNIFICANCE IN HEREDITY. 38 



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eggs, was probably the phyletic precursor of the present con- 

 dition. I imagine that the division of the mature cgg-ccll— 

 although it is now so extremely unequal— was equal in very 

 remote times ; but that for reasons of utility, connected with 

 the specialization of the eggs of animals, it gradually became 

 more and more unequal. It is now hardly possible to give in 

 detail the various reasons of utility which have brought about 

 this condition, but it may be assumed that the enormous size 

 attained by many animal egg-cells has been especially potent 

 in producing the change. 



A careful consideration of this last point seems to me to be 

 demanded by a comparison of the egg-cells with the male 

 germ-cells. Just as the female germ-cells of animals are dis- 

 tinguished by the attainment of a large size, the male germ- 

 cells are generally remarkable for their minute proportions. 

 In most cases it would be physiologically impossible for a large 

 egg-cell, rich in yolk, to attain double its specific size in order 

 to undergo division into two equal halves and yet to remain of 

 the characteristic size. Even without the additional difficulties 

 imposed by the necessit}^ for such a division, all means— such 

 as cells used as food, or the passage of food from follicular cells 

 into the ovum, etc. — are emplo^'ed in order to bring the egg- 

 cell to the greatest attainable size. Furthermore, the 'reducing 

 division ' of the nucleus cannot take place before the Qg'g 

 has attained its full size, because the ovogenetic nucleoplasm 

 still controls the egg-cell, and must be removed before the 

 germ-plasm can regulate its development. By arguments 

 such as these I should attem.pt to render the whole subject 

 intelligible. 



But the case is entirely different witii the sperm-cells, which 

 are generally minute : here it is quite conceivable that a 

 ' reducing division ' of the nuclei may take place by an equal 

 division of the sperm-cells, occurring towards the end of the 

 period of their formation ; that is to say, in such a way that 

 both products of division remain sperm-cells, and neither of 

 them perishes like the polar bodies. But the other possibility 

 also demands consideration, viz. that the reducing division may 

 occur at an earlier stage in the development of sperm-cells. 

 At all events, the arguments adduced above, which proved 

 that the consequence would be a want of variability in the 



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