VESTIGIAL PARTS. 61 



convenience of employing the term vestigial ; there can 

 be little doubt that its hind limbs are remnants. 



The combined effects of enlargement from increased 

 use, suppression, and change of function, has been to 

 produce in complex organisms a large number of ves- 

 tigial parts. Since Darwin considered the matter our 

 knowledge of such parts has increased greatly, and 

 in this chapter a few of the more important will be 

 considered, especially those which lead to pernicious 

 consequences. 



Before entering upon this subject in detail it is neces- 

 sary to make a few remarks on what are termed useless 

 parts. It is very essential that care be exercised before 

 pronouncing any part to be useless, for, as Mr. Wallace 

 truly remarks, " much of what we suppose to be useless 

 is due to our ignorance." It also becomes important 

 to inquire why such supposed useless organs are per- 

 petuated, seeing that disuse of a part tends to promote 

 its disappearance, Darwin was ot opinion that what 

 he termed " rudimentary organs are eminently variable, 

 and this is intelligible, as they are useless, or nearly 

 useless, and consequently no longer subjected to natural 

 selection. They often become wholly suppressed. When 

 this occurs they are nevertheless liable to occasional 

 reappearance through reversion." Subsequently Darwin 

 seems to have changed his opinion somewhat, for in the 

 fifth edition of the " Origin of Species " he states, in 

 reference to adaptive changes of structure, " But I am 

 convinced from the light gained during even the last 

 few years that very many structures which now appear 

 to us useless will hereafter be proved to be useful and 



