VI.] SPECIES AND TIME. 147 



that so few instances tending to indicate its mode of origin 

 should have presented themselves. Here, as in the bats, 

 we might surely expect that some relics of unquestionably 

 incipient stages of its development would have been left. 



SKELETON OF A PLESIOSAUBIT8. 



The singular order Chelonia, including the tortoises, 

 turtles, and terrapins (or fresh- water tortoises), is another 

 instance of an extreme form without any, as yet known, 

 transitional stages. Another group may be finally men- 

 tioned, viz., the frogs and toads, anourous Batrachians, of 

 which we have at present no relic of any kind linking them 

 on to the Eft group on the one hand, or to reptiles on the 

 other. 



The only instance in which an approach toward a series 

 of nearly-related forms has been obtained is the existing 

 horse, its predecessor Hipparion, and other extinct forms. 

 But even here there is no proof whatever of modification 

 by minute and infinitesimal steps ; a fortiori no approach 

 to a proof of modification by " Natural Selection," acting 

 upon indefinite fortuitous variations. On the contrary, the 

 series is an admirable example of successive modification 

 in one special direction along one beneficial line, and the 

 teleologist must here be allowed to consider that one mo- 

 tive of this modification (among probably an indefinite 

 number of motives inconceivable to us) was the relation- 



