August 14, 1896.] 



SCmNGE. 



183 



ticular cases, while others are difficulties 

 that further investigation may hope to re- 

 move, not insurmountable obstacles. Every 

 year new forms are discovered and better 

 material of known forms. Though the 

 White Eiver Bad Lands have for more than 

 half a century been classic collecting ground, 

 hardly a season passes that several new 

 genera are not registered from there, and, 

 better still, types before known only from 

 fragments are gradually made more and 

 more complete. From the middle Eocene 

 to the lower Miocene there is in the West 

 an almost unbroken transition which is 

 bringing forth a truly magnificent series of 

 evolutionary stages. 



While paleontology, as we have seen, does 

 not profess to give an unbroken life history 

 of the earth, yet it has certain preeminent 

 advantages which neither comparative 

 -anatomy nor embryology possesses, and 

 which fit it to form an invaluable supple- 

 anent to those other methods of morpho- 

 logical investigation. 



(1) In the first place, it gives us in many 

 cases actual phyletic series in their true or- 

 der of succession in time. In many groups 

 of animals we have already recovered phy- 

 letic series so full, so complete, that no ob- 

 server can hesitate to accept them as repre- 

 senting actually or very nearly the succes- 

 sive steps of evolutionary change in the or- 

 der in which they occurred. Little confi- 

 dence may, perhaps, be placed in these 

 phyla by those who have not made a special 

 study of them, and it may be imagined that 

 fuller knowledge will require them to be 

 completely changed. But when we find 

 such a series as that of the horses, leading- 

 back by almost imperceptible gradations 

 from the great monodactjd living forms to 

 their little five-toed progenitors in the far 

 distant Eocene times, doubt becomes well- 

 nigh impossible. A limit of error is placed 

 by the stratigraphical order, the geological 

 and morphological successions coinciding 



beautifully. AVhatever changes in the details 

 of such a series may be needed, a radical re- 

 construction of it is not in the least likely to 

 be called for. Few observers, if any, would 

 now uphold the arrangement of the equine 

 phylum proposed by Kowalevsky, namely, 

 Palceotherium, Anchitherium, Hipparion, 

 Equus ; and yet it is surprising to see how 

 the general character of this series, and the 

 deductions as to the manner of evolution 

 which may be drawn from it, agree with 

 those made on the basis of the equine se- 

 ries as we now have it. Kowalevsky's mis- 

 take merely consisted in putting certain 

 members of the side branches into the main 

 line of descent, and that similar errors have 

 been made in accepted phylogenies is not at 

 all unlikely. The correction of such errors 

 will, however, change the general result but 

 little, and we may appeal with considerable 

 confidence to the conclusions which legiti- 

 mately follow from a study of these phy- 

 logenies. 



Fortunately, the well-defined phyletic 

 series which have already been made out 

 occur in very widely separated animal 

 groups — mammals, reptiles, cephalopods, 

 brachiopods, echinoderms, etc. — so that the 

 points in which they agree are apt to prove 

 of general application and validity. The 

 cephalopods are particularly valuable in 

 this connection, because in them the em- 

 bryonic and young stages of the shell are 

 preserved in the adult, and thus conclusions 

 have a distinct support from embryological 

 considerations. To recur to the linguistic 

 analogy, we have here at least fragments, 

 and sometimes very extensive ones, of the 

 various literatures which register the 

 changes of language, and in the original 

 documents which bear evidence of their 

 dates and succession, and which, however 

 incomplete, have not been falsified by 

 forgeries and late interpolations. In this 

 way we may establish unequivocally some, 

 at least, of the animal pedigrees, which it is 



