606 THE POPULAR SCIENCE MONTHLY. 



lows that the history of the succession of life is recorded with the 

 same regularity, and may be read by those who will bestow the neces- 

 sary labor upon it. 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 species 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 ani- 

 mals with skeletons, or vertebrata, but it has given us many of them. 

 To take the vertebrata, we have obtained the long-since extinct ances- 

 tor of the very lowest vertebrates. Then we have discovered the an- 

 cestor of the true fishes. We have the ancestor of all the reptiles, 

 of the birds, and of the mammals. If we considered 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. We have the primitive mammals from which all these kinds 

 that I have mentioned drew their descent, and from which, no doubt, 

 many other lines were derived which we have not yet discovered in 

 North America. Such are the lines of the elephants, the hyenas, the 

 bears, the hogs, and the oxen. The ancestors of the strange, pouch- 

 bearing marsupialia, have been found in part. These creatures, now 

 confined (except the opossums) to Australia and the adjacent islands, 

 were, at an early period, widely distributed over the earth. Some of 

 these are found in the fossiliferous deposits of our plains and Rocky 

 Mountains. 



So soon as the possibility of learning the manner of creation of 

 animals is admitted, curiosity and speculation are awakened. Many 

 alternatives naturally occur to the mind. Were any of the living 

 kinds of animals descended from any other living species, or have the 

 ancestral animals all disappeared from the earth ? Have the giants of 

 ancient periods become reduced in size and strength, or have the giants 

 of to-day grown from weak and insignificant beginnings ? Have 

 things grown more and more perfect with the lapse of the ages, or 

 have they degenerated from more perfect ancestors ? Have these 

 changes advanced alike in all continents, or have they proceeded differ- 

 ently in different parts of the earth ? Such are the questions that 

 confronted the student of North American vertebrate paleontology 

 fifteen years ago, and some of them could only be answered by North 

 American material, not only because its record is the most complete, 

 but because, as the second continent studied, it furnished the first 

 opportunity in the history of the science for a comparison with the 

 record already placed before us by the paleontologists of Europe. 



