146 



THE GENESIS OF SPECIES. 



[CUAI'. 



or tliree can be selected as examples. Thus those remark- 

 able fossil reptiles, the Ichthyosauria and Plcsiosauria, ex- 



THE ABCUEOPTERYX (OF TUE OOLITE 8TKATA). 



tended, through the secondary period, probably over the 

 greater part of the globe. Yet no single transitional form 

 has yet been met witli in spite of the nuiltitudinous indi- 

 viduals preserved. Again, with their modern representa- 



. j^ltfU'* 



.^^ 



BKKl.KTON OV AN ICllTlIYUHAt'UUtt. 



tives, the Cetacea, one or two aberrant forms alone have 

 been found, but no series of transitional ones indicating 

 minutely the line of descent. This group, the whales, is" a 

 very marked one, and it is curious, on Darwinian principles, 



