l82 COXTINUITV OF THE GERM- PLASM AS THE [IV. 



plasm once contained and still contains the gcrm-nucleoplasm 

 of the grandparents as well as that of all previous generations. 

 It is obvious that the nucleoplasm of each antecedent genera- 

 tion must be represented in any germ nucleus in an amount 

 which becomes less as the number of intervening generations 

 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 

 descendants. Thus while the germ-plasm of the f^ither 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 yyljj, and 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-bod}'. 



Strasburger — supported by van Beneden's observations, but 

 in opposition to the opinions of the latter— had already ex- 

 plained, in a manner similar to that described above, the 

 process by which the hereditary transmission of certain cha- 

 racters takes place, and to this extent our opinions coincide. 

 The nature of heredity is based upon the transmission of 

 nuclear substance with a specific molecular constitution. This 

 substance is the specific nucleoplasm of the germ-cell, to which 

 I have given the name of germ-plasm. 



O. Hertwig' has also come to the same conclusion: at an 



' O. Hertwig, * Das Problem der Befruchtung und dcr Isotropic des 

 Eies.' Jena, 1885. 



