324 MY LIFE [Chap. 



structure and development of the lower forms of animal life. 

 From that time I always looked up to Huxley as being 

 immeasurably superior to myself in scientific knowledge, and 

 supposed him to be much older than I was. Many years 

 afterwards I was surprised to find that he was really younger. 



About this time I read before the same Society a few 

 notes on the species of monkeys I had observed on the 

 Amazon, either wild or in a state of captivity, with the par- 

 ticular object of pointing out their peculiarities of distribu- 

 tion. As with butterflies and many birds, I found that both 

 the Amazon and the Rio Negro formed the limit to the 

 range of several species. The rare monkey, Lagothrix Hum- 

 holdti, inhabits the district between the Rio Negro and the 

 Andes, but is quite unknown to the east of that river. A 

 spider-monkey {Ateles paniscus) is found in the Guiana dis- 

 trict up to the Rio Negro, but not beyond it. The short- 

 tailed Brachiurus Couxiu has the same range, while distinct 

 species are found in the Upper Amazon and the Upper Rio 

 Negro. The two species of sloth-monkeys {Pithecid) are 

 found one to the north, the other to the south of the Upper 

 Amazon. In several other cases also, as well as with the 

 beautiful trumpeters among birds, the great rivers are found 

 to form the dividing lines between quite distinct species. 

 Four great divisions of eastern equatorial America, which 

 may be termed those of Guiana, Ecuador, Peru, and Brazil, 

 are thus distinctly marked out by the Amazon and its great 

 northern and southern tributaries — the Rio Negro and the 

 Madeira river ; and it seems easy to account for this if we 

 look upon the vast central plains of South America, so little 

 elevated above the sea-level, as having been formerly a gulf 

 or great inland sea which has been gradually filled up by 

 alluvial deposits from the surrounding highlands, and to have 

 been all stocked with forms of life from the three great 

 land-masses of the continent. These would be diversely 

 modified by the different conditions of each of these areas, 

 and as the intervening seas became formed into alluvial 

 plains drained by a great river, that river would naturally 



