the species, although extremely numerous (about 300 are known in collections), are nearly all very rare. It is worthy of note that mimicking insects are very generally of great scarcity; that is, few examples of each species occur in the places where they are found, and they constitute groups which are remarkable for the strongly-marked diversity and limited ranges of their species.
After we had rested some weeks in Barra, we arranged our plans for further explorations in the interior of the country. Mr. Wallace chose the Rio Negro for his next trip, and I agreed to take the Solimoens. My colleague has already given to the world an account of his journey on the Rio Negro, and his adventurous ascent of its great tributary the Uapés. I left Barra for Ega, the first town of any importance on the Solimoens, on the 26th of March, 1850. The distance is nearly 400 miles, which we accomplished in a small cuberta, manned by ten stout Cucama Indians, in thirty-five days. On this occasion, I spent twelve months in the upper region of the Amazons; circumstances then compelled me to return to Pará. I revisited the same country in 1855, and devoted three years and a-half to a fuller exploration of its natural productions. The results of both journies will be given together in subsequent chapters of this work; in the meantime, I will proceed to give an account of Santarem and the river Tapajos, whose neighbourhoods I investigated in the years 1851–4.
A few words on my visit to Pará in 1851, may be
