20 NATURAL INHERITANCE. [chap. 



watch their grouping, and we know nothing directly 

 about them, but we may gain some idea of the various 

 possible results by noting the differences between the 

 brothers in any large fraternity (as will be done further 

 on with much minuteness), whose total heritages must 

 have been much alike, but whose personal structures 

 are often very dissimilar. This is why it is so im- 

 portant in hereditary inquiry to deal with fraternities 

 rather than with individuals, and with large fraternities 

 rather than small ones. We ought, for example, to 

 compare the group containing both parents and all the 

 uncles and aunts, with that containing all the children. 

 The relative weig-ht to be assigned to the uncles and 

 aunts is a question of detail to be discussed in its 

 proper place further on (see Chap. XL) 



Stable Forms. — The changes in the substance of the 

 newly-fertilised ova of all animals, of which more is 

 annually becoming known, : indicate segregations as 

 well as aggregations, and it is reasonable to suppose 

 that repulsions concur with affinities in producing 

 them. We know nothing as yet of the nature of 

 these affinities and repulsions, but we may expect them 

 to act in great numbers and on all sides in a space 

 of three dimensions, just as the personal likings and dis- 



1 A valuable memoir on the state of our knowledge of these matters up 

 to the end of 1887 is published in Vol. XIX. of the Proceedings of the 

 Philosophical Society of Glasgow, and reprinted under the title of The 

 Modern Cell Theory, and Theories as to the Physiological Basis of Heredity, 

 by Prof. John Gray McKendrick, M.D., F.R.S., &c. (R. Anderson, Glasgow, 

 1888.) 



