152 EVOLUTION OF TO-DAY. 



vertebrates by six stages, every one of which he 

 acknowledges to be hypothetical. 



Here, again, it would seem that embryologists had 

 abandoned a definite position for an indefinite 

 one ; but a little thought will show that this latter 

 position is the true one. If evolution is true, ani- 

 mals are continually changing, either slowly or by 

 occasional rapid advances, and that any single form 

 should retain its specific characters for a great (geo- 

 logically speaking) length of time, would be the ex- 

 ception and not the rule. These hypothetical stages 

 which we are considering must have disappeared 

 very long ago. To be sure, as already pointed out, 

 time does not necessarily imply change, but in these 

 cases we know the change has taken place. The 

 very fact that the ancestor of man became modified 

 in two directions, one toward man and the other 

 toward the monkey, would preclude us from finding 

 any representative of this ancestor living. Connect- 

 ing links will, therefore, almost always disappear. 

 Although living links between different groups are 

 occasionally found, it is hardly probable that they 

 represent the true ancestral forms. The demand 

 for the " missing link," once considered so great an 

 argument against evolution, ceases to be of any 

 significance with this understanding. 



But, nevertheless, granting all of this, it is evident 

 that these hypothetical ancestors must have existed 

 at one time, if the descent theory be true. Have 

 they left no trace? If we can find no living repre- 

 sentatives of them, we certainly ought to find them 

 represented by fossils. We are thus brought back 



