370 LOUIS AGASSIZ. 



between organized beings." Following this 

 comparison closely, lie shows how the early 

 embryonic condition of the present fishes is 

 recalled by the general disposition of the fins 

 in the fishes of the Old Red Sandstone, and 

 especially by the caudal fin, making the un- 

 evenly lobed tail, so characteristic of these 

 ancient forms. This so called heterocercal 

 tail is only known to exist, as a permanent 

 adult feature, in the sturgeons of to-day. The 

 form of the head and the position of the 

 mouth and eyes in the fishes of the Old Red 

 were also shown to be analogous with embry- 

 onic phases of our present fishes. From these 

 analogies, and also from the ascendency of 

 fishes as the only known vertebrate, and there- 

 fore as the highest type in those ancient de- 

 posits, Agassiz considered this fauna as repre- 

 senting " the embryonic age of the reign of 

 fishes ; " and he sums up his results in conclu- 

 sion in the following words : " The facts, taken 

 as a whole, seem to me to show, not only that 

 the fishes of the Old Red constitute an inde- 

 pendent fauna, distinct from those of other 

 deposits, but that they also represent in their 

 organization the most remarkable analogy with 

 the first phases of embryonic development in 

 the bony fishes of our epoch, and a no less 



