NO TRANSMUTATION OF SPECIES. 395 
which Geology takes cognizance, of that 
systematic and uniform arrangement of the 
Animal Kingdom, under which every family is 
nearly connected with adjacent and cognate fa- 
niilies. Three of the families under considera- 
tion are among the present inhabitants of the 
"^ater, while the fourth has been long extinct, 
and occurs only in a fossil state. When we see 
tile most ancient Trilobites thus placed in imme- 
liiate contact with our living Crustaceans, we 
nannot but recognize them as forming part and 
parcel of one great system of Creation, connected 
through its whole extent by perfect unity of 
design, and sustained in its minutest parts by 
nninterrupted harmonies of organization. 
We have in the Trilobites an example of that 
peculiar, and, as it is sometimes called, rudi- 
iiientary development of the organs of locomotion 
la the Class Crustaceans, whereby the legs are 
iiiade subservient to the double functions of 
paddles and lungs. The advocate for the theory 
af the derivation of existing more perfect species, 
successive changes from more simple ancient 
forms, might imagine that he sees in the Trilo- 
^ite the extinct parent stock from which, by a 
Series of developments, consecutive forms of more 
Perfect Crustaceans may, during the lapse of ages, 
^ave been derived ; but according to this hypo- 
thesis, We ought no longer to find the same simple 
Condition as that of the Trilobite still retained in 
