REVERSION 115 



individual, at least in so far as the characters common to 

 the race are concerned. On these lines the explanation of 

 the many cases of reversion to an ancestral character is not 

 that an entity representing those characters has lain dormant 

 in the individuals of many generations, but that the indi- 

 vidual in which they appear has stopped short, at a certain 

 point in the recapitulation of the life-history of its parents 

 and ancestry, and exhibits characters of a more or less re- 

 mote progenitor. Instead of recapitulation going on as far 

 as it did in the parents, it has ceased at a definite point, and 

 the later stages are simply missed altogether. The indi- 

 vidual therefore exhibits the characters of a more or less 

 remote ancestor in whom the recently developed characters 

 had not been superimposed upon the older ones. 



The cases quoted of the reappearance in domesticated 

 races of the characters of the wild- ancestor involve only 

 the reappearance of a character that has been absent for a 

 comparatively few generations and which is comparatively 

 recent. There are other cases in which the characters of 

 much more remote ancestors reappear in the offspring. The 

 ancestor of the modern horse (the Hipparion) possessed three 

 fully formed toes. The modern horse possesses only one. 

 In the embryo of the horse, we find a stage in which there 

 are three toes on each limb, just as well developed as in the 

 ancient Hipparion. As development goes on the two outer 

 toes disappear and only one remains functional. Thus, 

 when a foal is born it possesses only the one functional toe 

 of the modern horse. Occasionally, however, a foal appears 

 with two toes, and more rarely with three. Now, the dis- 

 appearance of the two outer toes is obviously a late addition 

 to the life-history of the modern horse, and the simplest 

 explanation of the occurrence of a foal with more than one 

 toe upon each limb, seems to be that the later stages have 

 been dropped in the case of such an individual. It is, in 

 fact, easier to interpret this phenomenon by supposing that 

 the toes which are normally developed in the embryo, con- 

 tinue in a few rare cases owing to failure of complete- 



