8 HEREDITY AND INHERITANCE 



view of this progress towards greater precision and simplification 

 of phraseology, it cannot be a matter for surprise that a biologist 

 should affirm that to speak of the " Principle of Heredity " in 

 organisms is like speaking of the " Principle of Horologity " in 

 clocks. The sooner we get rid of such verbiage the better for 

 clear thinking, since heredity is certainly no power, or force, 

 or principle, but a convenient term for the relation of organic 

 or genetic continuity which binds generation to generation. 

 Ancestors, grandparents, parents are real enough ; children 

 and children's children are also very real ; heredity is a term 

 for the relation of genetic continuity which binds them together. 

 We study it as a relation of resemblances and differences which 

 can be measured or weighed, or in some way computed ; as a 

 relation which is sustained by a more or less visible material basis 

 — namely, the germinal matter 



§ 3. Heredity and Inheritance in Relation to other Biological 



Concepts 



DeYelopment. — All living creatures arise from parents more 

 or less like themselves. The reproduction may be asexual, — by 

 fission, fragmentation, budding, and similar processes ; or 

 sexual, — by special germ-cells or gametes, which usually unite 

 in pairs (fertilisation or amphimixis) to start a new individual 

 body. Whatever the mode of reproduction may be — and that is 

 a long story by itself — there is a hereditary relation, a genetic 

 continuity. It is the business of the theory of heredity to inquire 

 into the precise nature of this genetic relation in the diverse 

 modes of reproduction. In what relation, for instance, does a 

 liberated germ-cell or gamete stand to the body which liberates 

 it ? In what relation does a fertilised ovum stand to the germ- 

 cells of the body into which it develops ? What contribution 

 does each parent make to the inheritance ? Do ancestors also 

 make contributions, and if so, how ? To answer this kind of 

 question is the business of the theory of heredity. 



