THE SILURIAN BEACH. 
41 
alteration in tlie mode of respiration, of repro- 
duction, of circulation, or in any of the systems 
of organs which characterize the more compre- 
hensive groups of the Animal Kingdom, although 
they are quite as much under the immediate in- 
fluence of physical causes as those structural fea- 
tures which have been constantly changing. 
The woody fibre of the Pine-trees has had the 
same structure from the Carboniferous age to 
this day, while their mode of branching and the 
forms of their cones and leaves have been differ- 
ent in each period according to their respective 
species. The combination of rings, tae structure 
of the wings, and the articulations of the legs 
are the same in the Cockroaches of the Carbon- 
iferous age as in those which infest our ships and 
our dwellings to-day, while the proportion of 
their parts is on quite another scale. The tissue 
of the Corals in the Silurian ago is identical in 
chemical combination and organic structure with 
that of the Corals of our modem reefs, and yet 
the extensive researches upon this class, for which 
we are indebted to Milne Edwards and Haime, 
have not revealed a single species extending 
through successive geological ages, but show us, 
on the contrary, that every age has had its own 
kinds, differing among themselves in the same 
way as those of the Gulf of Mexico differ now 
from those of the Indian Ocean and the Pacific. 
