174 Transmissibility of Modifications 



what we have said refers to the hormones of back- 

 boned animals. 



There are, as we have seen, a number of experi- 

 ments which must be taken seriously in connection 

 with the transmissibility of individually acquired 

 bodily modifications. Speaking for ourselves, we are 

 convinced by none, but that may be due to prejudice. 

 And why this prejudice? It is partly engendered by 

 the difficulty of thinking out a method by which an 

 extrinsic structural change in, let us say, the eye, or 

 the skin, or the skull, could specifically repercuss on 

 the germ-cells, changing them in a manner so repre- 

 sentative that the offspring not subjected to the 

 peculiar outside influence that played upon the 

 parents might yet show a peculiarity similar to that 

 which their parents acquired. Darwin suggested that 

 "gemmules" might pass from a modified corner of 

 the body to the germ-cells and serve as the vehicles of 

 specific change-producing stimuli, which would have 

 their effect when the germ-cells developed into off- 

 spring. Herbert Spencer had an analogous theory, 

 but both remained in the air and hypothetical. More 

 than that, they were h}^potheses invented to explain 

 what was not known to be a fact. 



But in 1908 a notable step was taken by Mr. J. T. 

 Cunningham, who published the suggestion that 

 bodily modifications due to peculiarities of nurture 

 might liberate specific hormones which would be 

 carried by the blood stream to the reproductive or- 

 gans, and there specifically affect the germ-cells in 

 such a way that the offspring reproduced something 



