PREFACE. 
IN the winter of 1865 it became necessary for me, on 
account of some disturbance of my health, to seek a change 
of scene and climate, with rest from work. Europe was 
proposed ; but though there is much enjoyment for a 
naturalist in contact with the active scientific life of 
the Old World, there is little intellectual rest. Toward 
Brazil I was drawn by a lifelong desire. After the death 
of Spix, when a student of twenty years of age, I had 
been employed by Martius to describe the fishes they 
had brought back with them from their celebrated Bra- 
zilian journey. From that time, the wish to study this 
fauna in the regions where it belongs had been an 
ever-recurring thought with me ; a scheme deferred for 
want of opportunity, but never quite forgotten. The fact 
that the Emperor of Brazil was deeply interested in all 
scientific undertakings, and had expressed a warm sym- 
pathy with my efforts to establish a great zoological 
museum in this country, aiding me even by sending 
collections made expressly under his order for the pur- 
pose, was an additional incentive. I knew that the head 
of the government would give me every facility for my 
investigations. Nevertheless, tempting as was the pros- 
