VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 29 



April llth. Last evening was the most beautiful we 

 have had since we left home ; perfectly clear with the 

 exception of soft white masses of cloud on the horizon, 

 all their edges silvered by the moonlight. We looked our 

 last for many months to come on the north star, and saw the 

 southern cross for the first time. With the visible image I 

 lost a far more wonderful constellation which had lived in 

 my imagination ; it has vanished with all its golden glory, a 

 celestial vision as amazing as that which converted Constan- 

 tine, and in its place stands the veritable constellation with 

 its four little points of light. 



The lecture to-day was upon the fishes of South America. 

 " I will give you this morning a slight sketch of the charac- 

 teristic fishes in South America, as compared with those of 

 the Old World and North America. Though I do not know 

 how the fishes are distributed in the regions to which we 

 are going, and it is just upon the investigation of this point 

 that I want your help, I know their character as dis- 

 tinguished from those of other continents. We must re- 

 member that the most important aim of all our studies in 

 this direction will be the solution of the question whether 

 any given fauna is distinct and has originated where it now 

 exists. To this end I shall make you acquainted with the 

 Brazilian animals so far as I can in the short time we have 

 before beginning our active operations, in order that you 

 may be prepared to detect the law of their geographical 

 distribution. I shall speak to-day more especially of the 

 fresh-water fishes. 



" In the northern hemisphere there is a remarkable group 

 of fishes known as the Sturgeons. They are chiefly found 

 in the waters flowing into the Polar seas, as the Mackenzie 

 River on our own continent, the Lena and Yenissoi in ilu- 



