The Evidence for Evolution 



other instances that might be quoted. One must indeed deal 

 carefully with such cases, for it is always difficult to say what 

 changes are new departures, and what are returns to ancestral 

 types. There is danger of arguing in a circle-^of supposing the 

 ancestry from the abnormality, and of terming the latter a re- 

 version because it suggests the supposed ancestry. Nevertheless, 

 when variations occur, suggesting characters which are believed. 



Fig. 9. 

 (a) The blind-gut of a kangaroo 

 {dl\ and (b) the correspond- 

 ing reduced structure, the 

 vermiform appendix in man 



Fig. 10. — Skeleton of Cassowary, show- 

 ing reduced wing-bones (a piece of 

 black paper is placed under them). 



From Dendy's Outlines of Ei'olutionary Biology (Constable). 



on other grounds, to be ancestral, they must tend to strengthen 

 the other evidence as to the evolution of the type in question. 



Another and a very strong evidence of Evolution is to be 

 found in what are termed vestigeal structures, two of which are 

 illustrated in Figs. 9 and 10. They are, for the most part, obviously 

 useless, and their occurrence has never been satisfactorily ex- 

 plained except by supposing them to be remnants of organs 



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