50 EVOLUTION 



pretation of these except as recapitulations of 

 the respiratory apparatus of remote aquatic 

 ancestors. 



Every one is familiar with the bony flat- 

 fishes, such as plaice, flounder and sole, which 

 have an asymmetrical body flattened from 

 side to side. They rest and swim on their 

 right or left side, which is unpigmented, and 

 both eyes are on the upturned pigmented 

 side. Now these markedly asymmetrical 

 fishes begin their life with perfect symmetry 

 just like other fishes. They retain this for 

 some considerable time and live near the 

 surface. At a certain stage a very remark- 

 able lop-sidedness of growth and alteration 

 of equilibrium sets in; they begin to sink 

 towards the bottom, the eye on the down- 

 turned side travels round, or even in part 

 through, the margin of the head; in short, a 

 metamorphosis occurs. Different natural- 

 ists may read different meanings into the 

 word ;< recapitulate," but in some sense it is 

 surely true that these flat fishes recapitu- 

 late in their early development the form of 

 symmetrical ancestors. 



We have already referred to the case of the 

 baleen whale, which has two sets of teeth in 

 embryonic life. They never cut the gum, 

 they are absorbed at a very early stage, they 

 are not of the slightest use. It appears to us 



