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- 



