74 



APES AND MONKEYS. 



the existence of forests that they have neither 

 crossed the Cordilleras nor extended to the 

 Antilles, which, nevertheless, were probably 

 connected in former times with the mainland, 

 though, no doubt, only by means of treeless 

 isthmuses. Most of the American Simiae 

 have never come down to the earth. They 

 have been born in the tops of the trees of the 

 primeval forest, there have lived, and have 

 ended their existence still hanging in death 

 to the branches. 



Now although the majority t)f Old World 

 Simiae, which have all the same dental formula 

 as man, live entirely among trees, even some 

 of the anthropoid apes, like the orangs and 

 gibbons, still leading such a life exclusively, 

 yet we see many adaptations to other con- 

 ditions of life. One may characterize the 

 chimpanzee and gorilla as well as the magot 

 as semi-arboreal forms. They sleep on the 

 trees, seek their nourishment partly in their 

 fruits, but remain just as much upon the 

 ground, where the former, at least, assume a 

 semi-erect position, and frequently, especially 

 in fighting, go upon only two feet. As 

 entirely terrestrial forms we may designate 

 the Macacus nemestrinus and all the baboons, 

 for, while they are able to clamber about 

 dexterously among the rocks on all fours, 

 and seek their nourishment, for the most 

 part, only on the ground, and, indeed, even 

 in the earth, they climb high trees but seldom, 

 and most of them prefer to frequent districts 

 quite destitute of trees. That high mountains 

 rising above the tree-line can form no barrier 

 to the distribution of terrestrial monkeys, as 

 it does to those of America, follows as a matter 

 of course. 



Yet the arboreal life seems even in the 

 Old World to have exercised an important 

 influence on the geographical distribution, 

 for all the arboreal forms of the Old World 

 are confined to their re.spective continents 

 and island groups. The members of the 

 genus Troglodytes (chimpanzee and gorilla), 

 the Colobi, and Cercopitheci are all restricted 



to Africa; the mias, gibbons, and Semnopi- 

 theci are found only in the Asiatic tropics; 

 the macaques are an Asiatic type, of which 

 only one species, the magot, has spread west- 

 wards along the borders of the Mediterranean. 

 The baboons, on the other hand, in spite of 

 their extension to Arabia, and in spite of the 

 occurrence of the black ape on the islands 

 of the Eastern Archipelago as far as Celebes, 

 appear to be an essentially African type. 

 But these two genera, the macaques, and still 

 more the baboons, distributed over both con- 

 tinents, are precisely the two which have 

 more and more abandoned arboreal habits of 

 life. 



Although sufficient evidence is forthcoming 

 to show that even at the present day the 

 various families of monkeys undertake migra- 

 tions, which are chiefly determined by the 

 want of food, and some species manifestly 

 lead a nomadic and vagabond life, yet these 

 migrations must be confined within pretty 

 narrow limits, and afford no explanation of 

 the striking distance of the black ape on the 

 one hand, and the magot on the other hand 

 from their present centres. 



To explain these facts, as well as the 

 absolute geographical separation of the Simiae 

 of the two hemispheres, and the absence of 

 all true monkeys on Madagascar and the 

 Antilles, we must recognize other causes as 

 the determining factors, and these we can 

 find only in tracing the origin of the different 

 forms. 



We now know, mostly, to be sure, only 

 through fragments of jaws containing teeth, 

 a considerable number of fossil Indo-European 

 and some few American monkeys. The 

 species belonging to the older Tertiary strata, 

 the Eocene, are doubtful, and it is only the 

 Middle and Upper Tertiaries as well as the 

 cave- and alluvial deposits that have yielded 

 undoubted simian remains. 



On a closer analysis of these fossil forms 

 the first result that is established as an in- 

 dubitable fact is, that the separation of types 



