VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 29 
April ~L4th. 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- 
tino, 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 Yenissei in the 
