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. 
