LECTUEE XXIII 



EXAMINATION OF THE HYPOTHESIS OF THE 

 TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 



Darwin's Pangenesis — Alleged proofs of functional inheritance — Mutilations not 

 transmissible — Brown-Sequard's experiments on Epilepsy in guinea-pigs — Confusion of 

 infection of the germ with inheritance, Pebrine, Syphilis, and Alcoholism — Does the 

 interpretation of the facts require the assumption of the transmission of functional 

 modifications? — Origin of instincts — The iintaught pointer — Vom Rath's and Morgan's 

 views — Attachment of the dog to his master — Fearlessness of sea-birds and seals on 

 lonely islands — Flies and butterflies — Instincts exercised only once in tlie course of 

 a lifetime. 



As I have already said in an earlier lecture, Darwin adhered to 

 Lamarck's assumption of the transmission of functional adaptations, 

 and perhaps the easiest way to make clear the theoretical difficulties 

 which stand in the way of such an assumption is to show how 

 Darwin sought to present this principle as theoretically conceivable 

 and possible. 



Darwin was the first to think out a theory of heredity which 

 Avas worthy of the name of theory, for it was not merely an idea 

 hastily suggested, but an attempt, though only in outline, at elaborating 

 a definite hypothesis. His theory of ' Pangenesis ' assumes that cells 

 give rise to special gemmules which are infinitesimally minute, and 

 of which each cell brings forth countless hosts in the course of its 

 existence. Each of these gemmules can give rise to a cell similar 

 to the one in which it was itself produced, but it cannot do this at 

 all times, but only under definite circumstances, namely, when it 

 reaches 'those cells which precede in order of development' those 

 that it has to give rise to. Darwin calls this the 'elective affinity' 

 of each gemmule for this particular kind of cell. Thus, from the 

 beginning of development there arises in every cell a host of gemmules, 

 each of which virtually represents a specific cell. These gemmules, 

 however, do not remain where they originated, but migrate from 

 their place of origin into the blood-stream, and are carried by it 

 in myriads to all parts of the body. Thus they reach also the ovaries 

 and testes and the germ-cells lying within these, penetrate into them, 

 and there accumulate, so that the germ-cells, in the course of life, 

 come to contain gemmules from all the Ivinds of cells which have 

 appeared in the organism, and, at the same time, all the variations 



