CAUSE OF HEREDITY 289 



When I helped load a wagon with concrete tile, I had to 

 stop and get a pair of gloves, because the rubbing of the 

 rough tile against the end of my fingers soon wore away 

 the protecting outer skin, and unless I had provided pro- 

 tection in some way, the tips of my fingers would soon 

 have started to bleed. The callous under your feet and 

 the sole leather in your shoes are produced for one and 

 the same purpose. The ground will not produce shoes 

 or callouses to cover your feet nor will the tile produce 

 gloves or the callous covering to protect your hands. 

 Man must produce the shoes and gloves and the cell must 

 produce the callous. 



We might again consider some of the sexual characters 

 referred to heretofore. Mr. Walker has the following to 

 say on that subject: "Secondary sexual characters are 

 those which though appearing in all individuals of the 

 same sex and not in those of the other sex are not con- 

 nected directly with the sexual function, that is, with re- 

 production. Such characters are the beard and voice of 

 a man and the antlers of the stag. There is a great deal 

 of evidence which suggests that the potentiality of pro- 

 ducing these characters is present in the individuals of 

 both sexes. Among mammals and birds we constantly 

 find that the characters of the young male are those of the 

 female minus of course a few special characters. The 

 plumage of the young cock pheasant is similar to that of 

 the adult female. A boy's voice is similar to that of a 

 woman. If during infancy the sexual glands are removed 

 from a male animal the male secondary sexual characters 

 do not appear. Not only are the physical characters such 

 as changing the voice and plumage inhibited, but mental 

 character such as pugnacity do not develop. There are 

 some direct experiments which suggest very strongly 

 that the appearance of the secondary sexual characters 



