VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 31 
their geographical distribution seems to exclude it. Take, 
for instance, the Hornpouts ; they are very few in the north- 
ern hemisphere, hardly ever occurring in those rivers where 
the Sturgeons abound, and they are very numerous in the 
southern hemisphere, in southern Asia, Australia, Africa, 
and South America, where the Sturgeons are altogether 
wanting. In South America the Siluroids everywhere exist 
with the Goniodonts, in all other parts of the world without 
them ; the Goniodonts being only found in South America. 
If these were the ancestors of the Silaroids in South Amer- 
ica, they were certainly not their ancestors anywhere else. 
If the Sturgeons were the ancestors of the Siluroids and of 
the Goniodonts, it is strange that their progeny should con- 
sist of these two families in South America, and in the Old 
World of the Siluroids only. But if all three had some 
other common ancestry, it would be still more extraordinary 
that its progeny should exhibit so specific a distribution upon 
the surface of our globe. The Siluroids lay very large eggs, 
and as they are very abundant in South America we shall 
no doubt have opportunities of collecting them. Of the re- 
production of the Goniodonts absolutely nothing is known. 
Of course the embryology of both these groups would have 
a direct bearing on the problem of their origin. 
"Another family very abundant in various parts of the 
world is that of the Perches. They are found all over Xorth 
America, Europe, and Northern Asia ; but there is not one 
to be found in the fresh waters of the southern hemisphere. 
In South America and in Africa they are represented how- 
ever by a very similar group, that of the Chromids. These 
two groups are so much akin that from their structure it 
would seem natural to suppose that the Chromids were 
transformed Perches ; the more so, since in the western 
