274 CLARKE— THE AGE OF THE EARTH. 



oldest term in the whole long series of rocks in which life has been 

 well preserved, and we here, in this year 1922 of the Christian era, 

 are unable to find that any progress has been made in the structure 

 of these creatures or along the direct line of their development and 

 succession. Their successors in time and place have adjusted, read- 

 justed, adapted, and readapted themselves without having produced 

 a creature of their tribes which can be called a more intricate or a 

 more perfect mechanism. 



And yet what has gone on in that vast interval of time from then 

 to now? The successive derivation of all intermediate types of life 

 have come into being. The trilobite Neolenus, from the viewpoint 

 of the paleontologist, stands for a tremendous conception of the vast- 

 ness of time behind it. This inconspicuous thing, standing back be- 

 hind us in the dim days of the Cambrian, stripped bare now by the 

 arduous labors of its discoverer, reveals a creature so highly special- 

 ized that it must have commanded uncountable ages for its production 

 by any such process of organic development as that to which we 

 paleontologists make our allegiance. The problem behind the Neo- 

 lenus is that of having developed out of the unicellular expression of 

 life, under favoring physical conditions and directive impulse, this 

 intricate and closely functioning organism. How long did it take? 

 I would like to put the problem to the experimental biologist : Given 

 an organism with a full equipment of motor and sensory nerves and 

 an elaborated digestive tract, with specific organs of circulation, re- 

 production, and of waste — is the distance greater from that starting 

 point to the specialized creatures of the present, ourselves if you will, 

 or from the nuclear cell (which we must hold to be not alone the seat 

 but the radial point of life) up to that marvelously specialized crea- 

 ture? Starts are slow, progress to be secure must be deliberate, the 

 momentum of the impulse must be acquired gradually, the passage 

 from a protozoan to a metazoan means the crossing of a deep moat, 

 the climbing of a high wall. But the directive once acquired, then 

 matters may go forward with acceleration. On the basis, then, of 

 the structure of this ancient trilobite alone, it is safe and probably 

 necessary to answer that Neolenus was farther away from the begin- 

 ning of life, very, very much farther away, in the highest probability, 

 than we of to-day are from Neolenus. 



