THE CONQUEST OF THE DRY LAND 189 



boy who has 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 pro- 

 portions 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 mil- 

 lions 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 conjec- 

 ture. 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 building up of the body, 

 a recapitulation much condensed and tele- 

 scoped 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. Evolu- 

 tion is not something done with; it is going 

 on. Thus the Robber-Crab is a shore-animal 

 in process of becoming terrestrial. 



