OLD TYPES AND NEW 197 



2. FALSE REVERSION 



"Around the term 'reversion/ " Bateson observes, 

 "a singular set of false ideas have gathered them- 

 selves." In proof of this statement there may be cited 

 at least five categories of apparent reversion which 

 properly ought not to be classed as true reversion. 



A. ARRESTED DEVELOPMENT 



Feeble-mindedness is not reversion to ancestral 

 forms of less intelligence, but an instance of arrested 

 development when, for some reason, the individual fails 

 to accomplish his normal cycle of development. 



Likewise harelip in man is not a case of reversion to 

 rabbit-like ancestors in which harelip is the normal 

 condition, but it is ordinarily due to an arrest or fail- 

 ure of certain embryonic steps essential to the develop- 

 ment of the usual form of human lip. 



B. VESTIGIAL STRUCTURES 



These are the vanishing remains of characters that 

 were formerly of significance. They do not represent 

 something latent that is now reappearing, for they 

 have never yet disappeared phylogenetically, and con- 

 sequently they cannot be regarded as true reversions. 



The muscles under the scalp which enable those 

 persons possessing them to wiggle the ears; the pala- 

 tine ridges in the roof of the mouth of many babies 

 and some adults which resemble the ridges in the roof 

 of a cat's mouth ; the vermiform appendix, a necessary 



