NATURE AND ORIGIN OF THE GERM-CEIIS 37 



the parent, which, like the parent, is endowed with the power 

 of growth. In virtue of this property it will assume, if it does 

 not already possess it, and if the conditions are approximately 

 similar, the exact form of the parent. It is a portion of the 

 parent ; it is endowed with the same property of growth ; the 

 wonder would be if it assumed any other form than that of the 

 parent." 



In asexual reproduction the resemblance of the offspring to the 

 parent tends to he very complete, and the reason for like producing 

 like is no puzzle, when the separated off-portion is a representative 

 sample of the whole organism. 



§ 5. Nature and Origin of the Germ-cells 



Re-statement of the Central Problem of Heredity. — ^The 

 central problem of inheritance is to measure the resemblances and 

 differences in the hereditary characters of successive generations, 

 and to arrive, if possible, at formulae which wiU sum up the facts, 

 such as Galton's Law of Ancestral Inheritance and Mendel's 

 Law. The central problem of heredity is to form some con- 

 ception of what is essential in the relation of genetic continuity, 

 which binds generation to generation. Weismann's theory 

 of the continuity of the germ-plasm is, in the first instance, 

 a theory of heredity, and as important as Galton's law of 

 inheritance. 



We know that almost every multicellular plant or animal has 

 the beginning of its individual life in the union of two germ-cells 

 (ovum and spermatozoon), and what must be found if the prob- 

 lem of heredity is to be illumined at all is some reason why 

 the germ-cells should have this power of developing, and of 

 developing into organisms which are on the whole like the 

 parents. In what respects are the germ-cells peculiar, and 



