394 GEOGRAPHICAL AXD GEOLOGICAL DISTRIBUTION, 



these boundaries ; they are, therefore, essentially tropical in habit. 

 To what extent, however, climate alone is efficient in determin- 

 ing this distribution still remains to be ascertained, as it is well 

 known that certain forms, most intimately related to species in- 

 habiting the torrid lowlands, ajopear to habituate themselves to 

 regions of opposite climatic conditions, or where a fairly rigourous 

 winter prevails. Semnopithecus schistaceus has been observed in 

 the Himalayas at an elevation of 11,000 feet, sporting among the 

 garlands of a winter's snow, while a second species of the same ge- 

 nus, S. Roxellanse, and a macaque (Macacus Thibetanus), steadily 

 inhabit the snow-clad mountains of Moupin, Thibet, at a nearly 

 equal altitude. The most northerly apes known are the two spe- 

 cies last mentioned, a species from Japan (Macacus sjieciosus), and 

 the Barbary ape of the Kock of Gibraltar (Macacus inuus), but it is 

 a little doubtful whether the last is truly indigenous to the region 

 which it now inhabits. The southern limit in the Old World is 

 the region about the Cape of Good Hope, the home of the chac- 

 mas. In the New World no form is positively known to pass north 

 of the twentieth parallel of latitude in Southern Mexico (Ateles vel- 

 lerosus, a species of spider-monkey), but it is by no means improb- 

 able that a more northerly extension may be reached by some spe- 

 cies;* the American forms being exclusively arboreal in habit, their 

 southern extension will necessarily be determined by the limit of 

 forest growth, which, excepting along the Andean slopes, is in about 

 the thirtieth parallel of latitude, beyond which line no monkeys 

 are known. 



It is a circumstance of some little importance, as bearing upon 

 geographical distribution in general, that certain continental isl- 

 ands, as the West Indies, apparently so well adapted in their natural 

 physical conditions to the development of the members of this group 

 of animals, should be entirely deficient in them ; the same holds true 

 with New Guinea, and, indeed, with the entire continent of Australia. 

 Madagascar, while largely supplied with the lemurs, or half-mon- 

 keys, is wholly wanting in the apes proper. Long-continued isola- 

 tion of the tracts under consideration is, doubtless, the primary, if 



* According to a statement of M. Rall(^, made some twenty -five years ago, 

 monkeys (probably a species of Ateles) •were found as far north as the upper 

 Tampico, or up to about latitude 23" (Sclater, " Nat. Hist. Keview," 1861, p. 

 509). 



