THE CONQUEST OF THE DRY LAND 189 



put his bleeding finger to his mouth knows that 

 the blood has a salt taste. And it is very 

 remarkable that the salts in the blood are in the 

 main the salts of the sea, and that they occur 

 in very much the same proportions as in 

 the sea. The correspondence becomes closer, 

 when we take into account the change in the 

 composition of the sea since blood was first 

 established millions and millions of years ago. 

 This tells a tale. 



We cannot turn back the hands of the world- 

 clock, and get it to strike over again the hours 

 that are past, but there is the rock-record to 

 help us to get away from conjecture. And, as 

 we have just seen, some help is to be got from 

 the individual development which is, in some 

 measure, in the making of organs and the build- 

 ing up of the body, a recapitulation much 

 condensed and telescoped of the history of the 

 race. 



We should also remember that some of the 

 changes we suppose to have occurred millions 

 of years ago have their counterparts in changes 

 that are taking place to-day. Evolution is not 

 something done with ; it is going on. Thus 

 the Robber-Crab is a shore-animal in process of 

 becoming terrestrial. 



