FOUNDATION OF A THEORY OF HEREDITY. 179 



Thus the nuclear substance must be the sole bearer of hereditary 

 tendencies, and the facts ascertained by van Beneden in the case of 

 Ascaris plainly show that tho nuclear substance must not only 

 contain the tendencies of growth of the parents, but also those of a 

 very large number of ancestors. Each of the two nuclei which 

 unite in fertilization must contain the germ-nucleoplasm of both 

 parents, and this latter nucleoplasm once contained and still contains 

 the germ-nucleoplasm of the grandparents as well as that of all 

 previous generations. It is obvious that the nucleoplasm of each 

 antecedent generation must be represented in any germ-nucleus in 

 an amount which becomes less as the number of intervening genera- 

 tions becomes greater ; and the proportion can be calculated after 

 the manner in which breeders, when crossing races, determine the 

 proportion of pure blood which is contained in any of the descend- 

 ants. Thus while the germ-plasm of the father or mother constitutes 

 half the nucleus of any fertilized ovum, that of a grandparent only 

 forms a quarter, and that of the tenth generation backwards only 

 TTTSTJ an d so on. The latter can, nevertheless, exercise influence'' 

 over the development of the offspring, for the phenomena of atavism 

 show that the germ-plasm of very remote ancestors can occasionally 

 make itself felt, in the sudden reappearance of long-lost characters. 

 Although we are unable to give a detailed account of the way in 

 which atavism happens, and of the circumstances under which it 

 takes place, we are at least able to understand how it becomes 

 possible ; for even a very minute trace of a specific germ-plasm 

 possesses the definite tendency to build up a certain organism, and 

 will develope this tendency as soon as its nutrition is, for some 

 reason, favoured above that of the other kinds of germ-plasm present 

 in the nucleus. Under these circumstances it will increase more 

 rapidly than the other kinds, and it is readily conceivable that a 

 preponderance in the quantity of one kind of nucleoplasm may 

 determine its influence upon the cell-body. 



Strasburger supported by van Beneden's observations, but in 

 opposition to the opinions of the latter had already explained, in 

 a manner similar to that described above, the process by which the 

 hereditary transmission of certain characters takes place, and to this 



lated by H. E. F. Garnsey, edited by I. B. Balfour, Oxford, 1887, p. 203, and 

 Douglas H. Campbell, ' Zur Entwicklungsgeschichte der Sperinatozoiden,' in Berichte 

 d. deutschen bot. Gesellschaft, vol. v (1887), p. 120. S. S.] 



N 2, 



