POLYPES. 
73 
structures of the Coral-worms very far excel the mightiest 
edifices of man. What was the impious project of Babel, 
what are the Pyramids of Egypt, compared with the coral 
reef of Australia — a barrier which extends almost ■without 
an interruption for a thousand miles ! 
The notion that the coral-rock was commenced in the 
fathomless depths of the ocean, and gradually reared to 
the surface, has been exploded by the discovery of Darwin, 
that the Coral-polypes cannot exist at a greater depth 
than some twenty or thirty fathoms. Our limited space 
will not permit us to do more than allude to his beautiful 
and ingenious theory, by which all the phenomena of coral 
formations are explained. It seems certain that every 
such structure must have been commenced on the inor- 
ganic rock ; and the slow subsidence of these in many 
instances has produced the various forms of atolls, or ring- 
islets enclosing lagoons, of barriers, and of fringing reefs. 
Most intelligent persons are acquainted with the more 
common forms of Madrepores or Corals. Whether exist- 
ing in massive, ramified, or laminated structures, they com- 
monly consist of a light porous stone, studded with shallow 
pits, in which are seen thin perpendicular plates radiating 
towards a centre. Sometimes instead of pits and a radiat- 
ing arrangement, the plates are set in rows in an involved 
and sinuated pattern. Now, during life, from amidst 
these plates rises up a gelatinous tissue bearing a mouth 
with protrusile lips, and an array of sensitive tentacles, 
all of which on alarm are contracted so as to disappear 
completely in the stony recesses, leaving nothing apparent 
but the white and apparently naked plates. Really, how- 
ever, they are not naked, but are still invested with a 
