294 RETROGRADE DEVELOPMENT. 
species derive less support, than from the pro- 
gression we have been tracing in the class of 
Fishes. The Sauroid Fishes occupy a higher 
place in the scale of organization, than the ordi- 
nary forms of bony Fishes ; yet we find examples 
of Sauroids of the greatest magnitude, and in 
abundant numbers in the Carboniferous and 
Secondary formations, wliilst they almost dis- 
appear and are replaced by less perfect forms 
in the Tertiary strata, and present only two 
genera among existing Fishes. 
In this, as in many other cases, a kind of re- 
trograde development, from complex to simple 
forms, may be said to have taken place. As 
some of the more early Fishes united in a 
single species, points of organization which, at 
a later period, are found distinct in separate 
families, these changes would seem to indicate in 
the class of Fishes a process of Division, and of 
Subtraction from more perfect, rather than of 
Addition to less perfect forms. 
Among living Fishes, many parts in the or- 
ganization of the Cartilaginous tribes, (e. g. the 
brain, the pancreas, and organs subservient to 
generation,) are of a higher order than the cor- 
responding parts in the Bony tribes ; yet we find 
the cartilaginous family of Squaloids co-existing 
with bony fishes in the Transition strata, and 
extending with them through all geological for- 
mations, unto the present time. 
