178 ORGANIC EVOLUTION CONSIDERED 



which serves as a lung. Amphibians have gills when 

 young, but afterwards acquire lungs. They generally, 

 but not always, lose the gills on arriving at maturity. 



All the higher vertebrates breathe by means of 

 lungs alone. 



From this brief statement we see some of the 

 various forms of breathing apparatus. 



It - is evident that these gills, air-tubes, sacs and 

 lungs, so various in position and different in struc- 

 ture, represent quite a number of separate evolutions, 

 if they were evolved at all. They cannot all have 

 been derived from any one primary form of breathing 

 apparatus. 



Gills, tracheae and lungs are widely apart in struc- 

 ture. Gills themselves, so different from each other 

 in structure and location must have had quite a num- 

 ber of independent origins. 



As to the origin of tracheae we know nothing. 

 It is evident, however, that they could not have been 

 evolved from gills. Insects, which breathe by means 

 of tracheae, we know appeared as early as the Lower 

 Silurian. We have no hint as to any possible method 

 of evolving their breathing apparatus. The appear- 

 ance of these highly organized air-breathing animals 

 at so early a period in the geological record is not in 

 harmony with the theory of evolution. 



With regard to the evolution of lungs, it is claimed 

 that the air-bladder of fishes is homologous to the 

 lungs of vertebrates. 



The Dipnoi, which are the highest order of fishes, in 

 addition to gills, have a cellular air-bladder which 

 performs the office of a lung, and it is claimed that 

 they show the transition from fish to amphibian. If 

 this is true, when did the Dipnoi originate? If their 

 lungs are of recent origin, then they show the evolu- 

 tion of lungs independently of each other at periods 



