INTRODUCTION. 



17 



old forms, resemble hoofed mammals, especially 

 Artiodactyla, in dentition. Even the placenta 

 bespeaks a close affinit}- to the latter. Very 

 probably, therefore, our present mode of division 

 unites in a single order animals which are derived 

 from quite diflerent ancestors, but which ha\-e 

 approached one another in respect of a number of 

 secondary characters. 



The same holds good also of the apes and 

 monke\-s, which cannot be deri\-ed from a single 

 ancestor. On their first appearance in the lower 

 Miocene the Simii-e of the New World are as 

 different from those of the Old as they are at the 

 present da\'. Moreover, there are Siniic'E which are 

 rather insectivorous in their habits, ^\•hile others 

 again approach more nearly the carnivorous and 

 omnivorous forms. 



We should thus have a group of ortlers, the Chir- 

 optera, Prosimii, and Simiae, which might, at least 

 in part, be placed \-er}' near the old Insectivora. 



Take now the Carnivora. ^^'c know even in 

 Jurassic strata marsupials \\hose dentition ap- 

 proaches the carnivorous type, and from more 

 recent strata, as well as the fauna of the present 

 era, we are acquainted with man_\-, \\hich, if we ma\- 

 so express oursel\-es, are more carnivorous than 

 the placental carnivores. The H}'a;nodons are an 

 unmistakable connecting link. The Carnivora are 

 accordingh" descended without doubt from mar- 

 supials. The seals, as we ha\-e already mentioned, 

 are only a branch of this group adapted to an 

 aquatic mode of life. 



The Perissodact}-la and Artiodactyla belong to 

 the Eocene nobilit\-. Ma}- we perhaps connect 

 them with the Jurassic genus Stereognathus.' 

 However that ma)- be, these two orders form, so 

 to speak, trees, \-\hose original trunks, the tapirs 

 and pigs, ha\-e continued on to our own da}-. 

 Both stems have put forth many branches now- 

 extinct, which we cannot here enumerate, but the 

 Solidungula and rhinoceroses form series which 

 ha\-e developed from the ancient Perissodact}-la, 

 the former from those of Eocene, the latter 

 those of Miocene times. \'er_\- probably the Pro- 

 boscidea and Sirenia are also to be reckoned to this 

 group. Further, there is probabl}- no doubt as to 

 the fact that the ruminants and hippopotamuses are 



descended from the first Artiodact\Ia, the pigs. In 

 these two great orders, also, the marked distinction 

 between the primiti\-e stocks of the Old and the 

 New World is plainh- manifest. 



The rodents of the Eocene nobilit_\- cannot be 

 traced with certaint\- from an\- marsupial term. 

 Onl_\-the genus Plagiaulax, from Jurassic times, ex- 

 hibits certain distant resemblances. The members 

 of this order ha\-e remained what thc\- were at first; 

 they ha\"e not essentialh' altered throughout the 

 whole geological period in which the}- are known. 



The same is the case 'with the edentates. This 

 group is manifestly made up of the descendants of 

 se\'eral ancestors; but we can onl}- trace them 

 back to the Pliocene, and in doing so we cannot 

 disco\"er any uncqui\'ocal relations to older t}-pes. 



From all this two main conclusions in our opinion 

 ma}- be drawn. First, that it is a perfcctl}- ground- 

 less h}-pothesis, that the mammals can all be traced 

 back to a single stock; and, second, that the \arious 

 original stocks, which we feel compelled to assume, 

 ha\'e de\-eloped, in the regions to which the}- are 

 confined, independentl}- of each other, and often in 

 such a manner that the ultimate forms which they 

 have attained ha\e more resemblance to each other 

 than the t}-pes from which the}- ha\-e proceeded. 



In the body of the present work we ha\e sub- 

 di\-ided the mammals in accordance ^\ith tlie points 

 of \iew which we have just explained, ^^'e follow 

 the series from the most perfect forms, those stand- 

 ing nearest to man, the Simla;, down to the t}-pes 

 with the lowest organization. The aplacental 

 forms, the marsupials and monotremes, were 

 obliged to take the last place; and among the 

 placental forms the edentates and rodents un- 

 doubted!}- form the lowest steps in the ladder. 

 After the Simla; the orders standing next to the 

 stem-group of the Insecti\ora, name!}- the Prosimii 

 and Chiroptera, naturally range themselves in im- 

 mediate succession, and then follow the Carni\-ora, 

 among ^\■hich the Pinnipedia (seals) form the 

 transition to the whales, with which again are con- 

 nected the Sirenia and Proboscidea as transitions to 

 the Even-toed Ungulates (Artiodact}-laV 



The table on page iS exhibits these subdi\-isions, 

 with their general characters, in the order in which 

 the\- are treated in the bod\- of the work. 



