THE PHENOMENA OF REVERSION ^;^;^ 



4. Reversion to Rudintentary Characters. 



It is well known that organs which have lost their value for 

 the preservation of the species become rudimentary in the course 

 of generations : they diminish in size, become stunted, and ulti- 

 mately disappear altogether. 



This may be expressed in terms of the idioplasm as follows. 

 The group of determinants in the germ-plasm for the organ in 

 question becomes reduced in one id after the other, first in one 

 determinant and then in another, until finally it disappears com- 

 pletely ; and the process is repeated in an increasing number of 

 ids, until eventually this group of determinants is no longer 

 contained in any of them. It cannot be stated how long a time 

 and how many generations are required for this process, but it 

 may at any rate be asserted, and even proved, that individual ids 

 still contain determinants for the organ in question long after its 

 disappearance from the mature individual. The fact that the 

 organ occasionally reappears, and that consequently reversion 

 may take place^ proves that this is the case. 



The siipeyjiiLnierary nipples which occasionally occnr in human 

 beings are an interesting example of this kind. The two normal 

 nipples generally occur in a rudimentary form in men, but, in 

 addition to these, very diminutive ones are occasionally met with 

 in parts in which they are normally present only in the lower 

 orders of mammals, such as carnivores, rodents, and lemurs : — 

 a pair may be present above the normal teats near the axillary 

 region, and two or three others lower dow^n on the abdomen. 

 All of them certainly never occur in the same individual, but 

 usually only a single one or a pair are present : these, however, 

 are found both in men and women. They are undoubtedly to 

 be looked upon as reversions to extremely remote characters 

 possessed by our lower mammalian forefathers. We owe an 

 accurate account of their occurrence in the male sex to the 

 numerous and detailed investigations of Otto Ammon,* who 

 found them in three per cent, of our recruits. 



As Amnion's researches only extend over two, or at most 

 three generations, and only refer to individual cases, we cannot 

 form a precise estimate as to the degree and extent to which 

 these structures are transmitted. We may, however, attribute the 



* I am indebted to Mr. Ammon for these details, which are not yet 

 published. 



