Chap. VI. VARIATION OF SPPXIES. 255 



lands, in contradistinction to the red-breasted species, 

 wliich are named Suruquas da terra firma. I often 

 saw small companies of half a dozen individuals quietly 

 seated on the lower branches of trees. They remained 

 almost motionless for an hour or two at a time, simply 

 moving their heads, on the watch for passing insects ; 

 or, as seemed more generally to be the case, scanning 

 the neighbouring trees for fruit; which they darted off 

 now and then, at long intervals, to secure, returning 

 always to the same perch. 



The species of mammals, birds, and insects found at 

 Obydos are, to a great extent, the same as those inhabit- 

 ing the well-explored tract of country lying along the 

 seacoast of Guiana. No other locality visited in the 

 Amazons region supplied, among its productions, so 

 large a proportion of Guiana forms. The four monkeys 

 already mentioned all recur at Cayenne. A general 

 resemblance of the species to those of Guiana is one of 

 the jDrincipal features in the zoology of the Amazons 

 valley ; but in the low lands a great number exist only 

 in the form of strongly modified local varieties ; indeed, 

 many of them are so much transformed that they pass 

 for distinct species ; and so they truly are, according 

 to the received definitions of species. In the somewhat 

 drier district of Obydos, the forms are more constant to 

 their Guiana types. "VVe seem to obtain here a glimpse 

 of the manufacture of new species in nature. The way 

 in which these modifications occur merits a few remarks. 

 I will therefore give an account of one very instructive 

 case which presented itself in this neighbourhood. 



