S16 SUDDEN APPEARANCE OF ALLIED SPECIES. 



of the apparently sudden appearance of a whole group of 

 species, is that of the teleostean fishes, low down, according 

 to Agassiz, in the Chalk period. This group includes the 

 large majority of existing species. But certain Jurassic and 

 Triassic forms are now commonly admitted to be teleostean; 

 and even some palaeozoic forms have thus been classed by 

 one high authority. If the teleosteans had really appeared 

 suddenly in the northern hemisphere at the commencement 

 of the chalk formation, the fact would have been highly 

 remarkable ; but it would not have formed an insuperable 

 difficulty, unless it could likewise have been shown that at 

 the same period the species were suddenly and simultane- 

 ously developed in other quarters of the world. It is almost 

 superfluous to remark that hardly any fossil fish are known 

 from south of the equator; and by running through Pictet's 

 Palaeontology it will be seen that very few species are known 

 from several formations in Europe. Some few families of 

 fish now have a confined range ; the teleostean fishes might 

 formerly have had a similarly confined range, and after hav- 

 ing been largely developed in some one sea, have spread 

 widely. Nor have we any right to suppose that the seas of 

 the world have always been so freely open from south to 

 north as they are at present. Even at this day, if the Malay 

 Archipelago were converted into land, the tropical parts of 

 the Indian Ocean would form a large and perfectly enclosed 

 basin, in which any great group of marine animals might be 

 multiplied ; and here they would remain confined, until some 

 of the species became adapted to a cooler climate, and were 

 enabled to double the southern capes of Africa or Australia 

 and thus reach other and distant seas. 



From these considerations, from our ignorance of the 

 geology of other countries beyond the confines of Europe 

 and the United States, and from the revolution in our 

 palseontological knowledge effected by the discoveries of 

 the last dozen years, it seems to me to be about as rash to 

 dogmatize on the succession of organic forms throughout the 

 world, as it would be for a naturalist to land for five minutes 

 on a barren point in Australia, and then to discuss the nuni< 

 ber and range of its productions. 



