SOURCES OF CHANGE 61 



functional "lungs" of the lobe-finned ganoids were 

 obviously not developed in response to the condi- 

 tions of terrestrial life, although they were an im- 

 portant adjunct to the successful attainment of 

 terrestrial habits. Lungs are associated with air 

 and air is available to swimming animals as well 

 as to terrestrial species, yet there appears to be no 

 peculiar need for lungs among the fishes and the 

 air has no peculiar power to cause the develop- 

 ment of lungs. However, many such structures 

 have developed in the past, and, once developed, 

 have been available for use and consequently have 

 become adaptive. It is possible to find other well 

 developed characters which are apparently without 

 adaptive value. Such are the brilliant colors of 

 some butterflies. The transverse ridges on the 

 shells of some lamellibranch molluscs and the sharp 

 keels on others are apparently of no fundamental 

 value to the individual. The fantastic projections 

 on some of the tree hoppers are not known to be 

 adaptive, nor are the spines on the legs of Hesperi- 

 oidea, since they may be present or absent in closely 

 related genera. 



To the extent that all characters are a product of 

 definite hereditary capacity responding to a definite 

 environmental stimulus, there is a similarity in the 

 origin of everything organic, but it is obvious that 

 a character which bears to the stimulus producing 

 it no relationship of importance to the organism is 



