VARIATIONS RESEMBLING REVERSIONS 129 



mean by reversion the re-expression of an ancestral character after 

 a period of latency, it is obviously a particular mode of inheritance. 

 From another point of view it is a variation, and due to some 

 unknown germinal conditions which permit a long-latent, but 

 never lost, character to re-assert itself. When we consider the 

 intricate reductions which occur in the maturation of the germ- 

 cells, and the not less intricate reinforcements involved in 

 amphimixis, it is not impossible to imagine how an ancient 

 latent character may come to the front again after many genera- 

 tions. 



But we have also to remember that, apart from reasser- 

 tions of what is relatively old, there is a continual emergence 

 of what is relatively new. What occurred once as a new variation 

 may occur again, and it is a certain fact that the same type of 

 variation occurs over and over again in varieties of different 

 species. How many red and blue flowers have white varieties ! 

 how many trees have weeping varieties ! how many Arthropods 

 show similar increase or decrease in the number of their joints ! 

 how many birds show albinism ! There are limits to the varia- 

 tions of the kaleidoscope, and to the kaleidoscope of variations. 

 Therefore it is always possible that a variation really occurring 

 de novo, and apart from latent characters, may happen to coincide 

 with an ancestral trait. It may be described as a reversion, but 

 it is really an independent variation. 



Supernumerary mammae occasionally occur in human being9 

 in both sexes. Ammon found them in 3 per cent, of German 

 recruits. They obviously suggest the several pairs of mammas which 

 occur in many mammals e.g. in the half -monkeys or Lemurs. 

 Weismann (1893, P* 333) sa y s > " They are undoubtedly to be looked 

 upon as reversions to extremely remote characters possessed by our 

 lower mammalian forefathers." But it seems simpler to regard 

 them as independent variations, comparable to many other ab- 

 normal multiplications of parts. They happen to suggest bygone 

 conditions, but that is probably all that we are warranted in saying. 



Polydactylism in man has been interpreted as a reversion to an 



9 



