MONKEYS. 79 



Species liavo been described under at least a dozen different names, but Dr. Slack admits only 

 five species as genuine. 



The Spider Monkeys, Ateles (Sapajou of Dr. Slack), are about as numerous in species, but their 

 range is a little more extensive. In addition to the countries where the Howling Monkeys arc 

 found, at least three of the species of Spider Monkej^s extend into Peru, east of the Andes. 



The second group of Cebio.e are less remarkably fitted for an arboreal life than the prehensile- 

 tailed species. Dr. Slack has divided them into those having the incisor teeth erect (the Cebi), and 

 those having them oblique and proclive (the Pitheci^^e). Their tads arc not prehensile, although long 

 and hairj' ; and although their quadrumanous structure still makes the forest a congenial abode, they 

 can also live on the ground, and some of them are specially adapted for a life among rocky 

 precipices. Some are active and diurnal ; others, as the Nyctipitiieci, are nocturnal, and pass 

 the day in sleep. About a score of species belonging to this section have been described, all 

 inhabiting the same range as the previous genera, but perhaps extending a little further south. 



Considering the vast extent of land in South America, its mammalian fauna is singularly meagre 

 and homogeneous. The Monkeys furnish a greater number of species than any other genus, and even 

 these we see are much fewer than is generally supposed. The most of them are found over a very 

 wide extent of territory, a circumstance no doubt due to the uniform character of the whole country ; 

 with exception of the high lands in Guiana and Brazil, and of course of the Andes, there is 

 little difference in the conditions of life of any part of the land, from the Gulf of Mexico to 

 the south of Brazil. 



Map 2 shows how slight a depression would make both Guiana and Brazil islands, and there is no 

 doubt that at some former period, not very distant in geological time, they were surrounded bj^ sea. 

 As the seas which then surrounded them are now replaced on the inland side by great rivers, one 

 woidd have expected a more decided difference between their j^Iammalian fauna than really exists. 

 The species differ, but the genera arc for the most part the same. ^Vlien we come to the lower 

 animals, we shall see that the insidar antecedents of these countries are more fully borne out by 

 their faunas. If the reader refers to the table of the geographical distribution of the Lagothrices 

 in the Appendix, which is copied from Dr. Slack's monograj^h,* he will see that out of four species 

 which inhabit one of these former islands, Guiana, there are three found in the adjacent part of 

 the other island. North Brazil, none of which, however, extend into South Brazil. We also see 

 that three out of the four extend from Guiana into Venezuela, and that two of them reach Ecuador. 

 One of these is also found in Peru and Bolivia. The same thing occurs with the Hystricid^e, every 

 species found in Guiana being also found in Brazil. On the other hand, the instances of separation 

 by the Amazon, already cited from Mr. Wallace's travels, and on the authority of Mr. Bates — and 

 others which will meet us as we go along — sufficiently show that a certain amount of isolation is 

 produced by these great rivers. 



Perhaps it may be said that the rivers should be no barrier to the Monkej's, insamuch as if they 

 cannot swim across them, they can tiu-n them by ascending to their sources, there being an uninter- 

 rupted highway of trees and branches all the way to the Andes. While the stream was still 

 small, it had entered the forests, and the trees would meet overhead, or where a giant fell he 

 would bridge the river. This is true, and the inference would be sound, but for one circumstance. 

 Supposing a nation of Monkeys to set out from Guiana to the sources of the Rio Negro, and thence to 



* Slack in '■ Proc. Nat. Scieu. rhilad." Nov. 18()2. 



