AMERICAN ZOOLOGISTS AND EVOLUTION. 105 



A parallel case may be seen in the increase in size of the brain in 

 the vertebrates, and conspicuously in the higher vertebrates, since their 

 first appearance in geological history. The individual brain clearly 

 varies in size, and it does not require a great effort to perceive how in 

 the long run the greater brain survives in the complex struggle for 

 existe'nce. Associated with the greater development, parts that were 

 freely used for locomotion before are now compelled to perform addi- 

 tional service, and through the law of use and effort, which all admit 

 as an important factor, organs are modified in structure, the anterior 

 portion of the body assumes a new aspect ; and it was on the character 

 of these parts and aspects that Professor Dana was led to formulate 

 his comprehensive and ingenious pnnciple of ccphalization. It is a 

 result and not a cause. And so I believe, thoiigh with great deference 

 to Cope and Hyatt, that the laws of acceleration and retardation, exact 

 parallelisms, inexact parallelisms, and still more inexact parallelisms, 

 and many other laws and theories advanced by these gentlemen, are 

 not causes but effects, to be explained by the doctrine of natural selec- 

 tion and survival of the fittest. 



The connecting links and intermediate forms v»'hich the skeptical 

 public so hungrily demand are continually being discovered. Great 

 gaps are being closed up rapidly ; but the records of this work, being 

 published in the journals of our scientific societies, are hidden from the 

 public eye as much as if they had been published in Coptic. So rapidly 

 have these missing links been established that the general zoologist 

 finds it difficult to keep up with the progress made in this direction. 

 He can hardly realize the completion of so many branches of the 

 genealogical tree. 



Professor Cope,* who has accomplished so much in this direction, 

 says ; "Those who have, during the last ten years, devoted themselves 

 to this study, have been rewarded by the discovery of the course of 

 development of many lines of animals, so that it is now possible to 

 show the kind of changes in structure which have resulted in the spe- 

 cies of animals with which we are familiar as living on the surface of 

 the earth at the present time. Not that this continent has given us 

 the parentage of all forms of animal life, or all forms of animals with 

 skeletons, or vertebrte, but it has given us many of them. To take the 

 vertebrata, we have obtained the long-since extinct ancestor of the very 

 lowest vertebrates. Then we have discovered the ancestor of the true 

 fishes. We have the ancestor of all the reptiles, of the birds, and of the 

 mammals. If we consider the mammals, or milk-givers, separately, we 

 have traced up a great many lines to their points of departure from very 

 primitive things. Thus we have obtained the genealogical trees of the 

 deer, the camels, the musk, the horse, the tapir, and the rhinoceros, of 

 the cats and dogs, of the lemurs and monkeys, and have important 

 evidence as to the origin of man." 



* '• Popular Science Monthly," vol. xxvil, p. 605. 



