lands, in contradistinction to the red-breasted species, which are named Suruquás 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 inhabiting 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 principal 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. We 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.
