ARRESTS OF DEVELOPMENT 125 



together again and restore the wild form. There has been no 

 mysterious re-awakening of long-latent characters. We may 

 still call what occurs a " reversion," but in cases like the above 

 our interpretation is no longer Darwinian. 



§ 4. Phenomena sometimes confused with Reversion 



It is impossible to read the fairly abundant literature without 

 recognising that many phenomena are labelled " reversions " on 

 the flimsiest of evidence. Let us try to make the conception 

 more definite by criticism and elimination of alleged instances. 

 In this criticism we have especially to bear in mind that the term 

 " reversion " is not merely descriptive of the direction which the 

 variation takes ; it implies that this direction — ancestor-wards 

 — is due to something that occurs in the early history of the germ- 

 cells. 



Arrests of Development. — Though popular travesties have 

 reduced a luminous idea to an absurdity, it remains in a general 

 way true that the individual development, especially in the stages 

 of organ-forming, is in some measure a recapitulation of the racial 

 history. Although it is more picturesque than accurate to speak 

 of " every animal climbing up its own genealogical tree," there 

 is a suggestive general resemblance between the stages in the 

 individual development of organs, such as heart, brain, and 

 kidneys, and the stages in the supposed racial evolution of 

 the same. 



Now, it not infrequently happens that the recapitulation is 

 notably incomplete, that the development of an organ stops 

 before the normal " finished form " has been attained. 



Through defective nutrition or other untoward conditions of 

 nurture, the expression of the inheritance is inhibited. The 

 organism is not able to perfect itself in all its parts ; not, we 

 suppose, through any germinal defect (as subsequent generations 

 may show), but simply because it was not sufficiently fed, or 



