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 Siluroids 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 North 

 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 



