LECTURE XXII 



SHARE OF THE PARENTS IN THE BUILDING UP 



OF THE OFFSPRING 



The ids are ' ancestral plasms ' — The reducing division brings about a diversity of 

 germ-plasm in the germ-cells — Bolles Lee's ' Neotaxis ' even in the primordial germ- 

 cells — Hacker's observations on the persistent distinctness of the maternal and paternal 

 chromosomes — Identical twins — The individuality is determined at fertilization — 

 Unequal share of the ids in the determination of the offspring — Preponderance of 

 one parent in the composition of the offspring — Certain ids of the ancestors remain 

 unchanged in the germ-plasm of the descendants — Struggle of the Biophors — Alterna- 

 tion of the hereditary sequences in the parts of the child — Eeversion — Datura-hybrids 

 — Zebra-striping in the horse — Three-toed horses— New experiments in hybridization 

 among plants by Correns and De Vries — Xenia. 



As far as the phenomena of regeneration and budding are con- 

 cerned, we have not been able to do much more than bring them 

 under a formula, which harmonizes with the germ-plasm theory. 

 But the case is different with the actual phenomena of inheritance 

 in the restricted sense, for instance, with regard to the transmission 

 of individual peculiarities from parent to child. Here the theory 

 really increases our insight and lets us penetrate deeper into the 

 causes of the phenomena ; it is here no longer a mere ' portmanteau- 

 theory.' 



We are well aware, especially from observation on ourselves, that 

 is, on Man, that the children of a pair often resemble one another 

 but are never alike, and that one child frequently resembles one 

 parent, another the other, while a third may exhibit a mingling 

 of both parents. How does this come about? Since the germinal 

 substance of both parents is derived from that of the ovum, from 

 which they themselves have arisen^ — ^and must therefore be the 

 same in all the germ-cells to which they give rise — new determinants 

 cannot be added, and old ones cannot be dropped out, and variation 

 of the determinants, the possibility of which is granted, would still 

 not directly bring about the familiar mingling of resemblances to 

 the two parents, but would at most give rise to something new and 

 strange. 



Here the theory helps to elucidate matters. We found ourselves 

 obliged to assume that the germ-plasm is composed of ids, that is, 



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