34 EXPERIMENTAL EVOLUTION LECT. 



those of the frog, as having been useful at some time, 

 when they were rendered efficient by the presence of 

 gill-arches and gills, the only difference being in this 

 last case, that they have been useful not some days or 

 weeks or months ago, not in the same individual at an 

 earlier stage of life, but in remote ancestors, and the 

 remote ancestors are the amphibians, and, further still, 

 the fishes. If any other intelligible explanation can 

 be given of the presence of these aortic arches in 

 reptiles, which never, at any stage of life, are gill- 

 breathers, we certainly shall listen to it with great at- 

 tention. But the argument does not stop here, and 

 things may be pushed further still. Useless as cir- 

 culatory organs, and useless as respiratory organs, 

 these aortic arches are not limited to adult amphibians 

 and reptiles ; we meet them in birds, in mammals, and 

 even in man himself. At an early stage of their de- 

 velopment the latter all have on the side of the neck 

 several gill-slits and aortic arches. Will some creationist 

 explain why these arches, most of which are destined to 

 disappear, put in this temporary appearance ? Evolu- 

 tionists explain it as we have briefly pointed out : 

 but creationists must explain in some way or other 

 the temporary presence of these arches of which the 

 larger part rapidly disappears, while the remainder goes 

 to build the principal blood-vessels which originate in 

 the heart. 



