VI.] THEIR SIGNIFICANCE IN HEREDITY. 377 



germ-plasms. The loops split longitudinally in a direction in- 

 dicated by the longitudinal line upon each of them. In B the 

 halves of the loops are seen to have moved to the opposite poles 

 of the spindle, so that there are not only six loops at each pole, 

 but also all the six combinations of ancestral germ-plasms. 



Perhaps some may be inclined to look upon direct nuclear 

 division as a ' reducing division,' but I believe that such a view 

 would be incorrect. It is only approximately true that the 

 nuclear thread is divided into two halves of equal quantity by 

 direct division, and exact equality would onl}'- happen as it were 

 accidentally ; so that we cannot speak of a perfectly equal dis- 

 tribution of the ancestral germ-plasm in the two daughter-nuclei. 

 But the ' reducing division ' must obviously effect an exactly 

 regular and uniform distribution of the ancestral germ-plasms, 

 although this does not imply that every ancestral germ-plasm 

 of the mother-nucleus would be represented in each of the two 

 daughter-nuclei. But if out of e.g. eight nuclear loops at the 

 equatorial plane, four pass into one, and the other four into the 

 other daughter-nucleus, each of the latter will contain an equal 

 number of ancestral germ-plasms, although different ones. This 

 is indeed part of the foundation of the theory, for the ' reducing 

 division ' must remove exactly half of the original number of 

 ancestral germ-plasms, and precisely the same number must 

 be replaced at a later period by the sperm-nucleus. This could 

 hardly be achieved with sufficient precision by direct nuclear 

 division. 



I now come to inquire whether the expulsion of the second 

 polar body is in reality, as I have already maintained, a reduc- 

 tion in the number of ancestral germ-plasms present in the 

 nucleus of the ^gg. The view itself is sufficiently obvious, and 

 it would supply an explanation of the meaning of the process 

 which is still greatly wanted ; but it will nevertheless be not 

 entirely useless to consider other possible theories. 



It would be quite conceivable to suppose that the youngest 

 egg-cells, which multiply by division, may undergo one 're- 

 ducing division ' in addition to the ordinary process. Of course 

 this should occur once only, for if repeated, the number of an- 

 cestral idioplasms in the nucleus of the germ-cell would undergo 

 a decrease greater than could be afterwards compensated by 

 the increase due to fertilization. Thus the number of ancestral 



