322 



The Study of Animal Life 



between reappearance due to inheritance and reappearance 

 due to similar conditions of life. 



Then there is a strange series of facts showing that an 

 organism may reproduce characteristics which the parents 

 did not exhibit, but which were possessed by a grandparent 

 or remoter ancestor. Thus a lizard in growing a new 

 tail to replace one that has been lost has been known to 

 grow one with scales like those of an ancestral species. To 

 find out a lizard's pedigree, a wit suggests that we need only 

 pull off its tail. When such ancestral resemblance in ordi- 



n - r ^^sa^t^^. 



Fig. 69. — Devonshire pony, showing the occasional occurrence of ancestral 

 stripes. (From Darwin.) 



nary generation is very marked, we call it " atavism " or 

 " reversion," but of this there are many degrees, and 

 abnormal circumstances sometimes force reversion even 

 upon an organism with a normal inheritance. A boy 

 " takes after his grandfather " ; a horse occasionally exhibits 

 stripes like those of a wild ancestor ; a blue pigeon like the 

 primitive rock-dove sometimes turns up unexpectedly in a 

 pure breed ; or a cultivated flower reverts to the simpler 

 and more normal wild type. So children born during 

 famine sometimes show reversions, and some types of 

 criminal and insane persons are to be thus regarded, 



