308 Explanation of Inheritance 



not prevented from passing at the proper moment of 

 their development to terrestrial life. "One could say 

 that this depends upon the amblystomal form being not 

 yet sufficiently fixed in the heredity of the species, since 

 the epigenesis resulting from this heredity does not yet 

 necessarily cause the appearance of the amblystomal form 

 so long as the conditions to which this form is adapted 

 are not realized." 227 



Finally the experiments of Cunningham on the colors 

 of flat fishes already quoted above, are well known. He 

 has shown that during their first metamorphoses, while 

 the pigment is still present on both sides, the action of 

 light artificially reflected upon the side of the fish which 

 is turned toward the bottom does not prevent the pigment 

 from disappearing even then from that side, so that in 

 this case the color passes rapidly through a retrograde 

 development. But a prolonged exposure to light pro- 

 vokes the reappearance of the pigment on the lower side, 

 and the pigment spots are in every respect like those 

 which are normally present on the upper side of the 

 fish. 228 



In this experiment then one has a clear and direct 

 instance of a functional stimulus reinforcing the onto- 

 genetic stimulus. We say "reinforcing" because the fact 

 that the spots now appearing on the lower side are like 

 those above, demonstrates that they are not produced 

 de novo by the functional stimulus, but even now depend 

 upon the ontogenetic stimulus, which, with the help of 



22T Le Dantec: Traite de Biologic. P. 403-404. 



228 Osborn: The hereditary Mechanism and the Search for the 

 unknown Factors of Evolution. Biol. Lect. at the Mar. Biol. Lab. of 

 Wood's Roll, Summer Session 1894. Boston, U. S. A., Gin-n, 1896. 

 P. 91. 



