284 ~ LHE ATLANTIC. [cHAP. Iv. 
of tentacles and their high coloring, are so prominent that they 
entirely mask the coral ; but in a few—as, for example, in a brain- 
coral, Diploria cerebriformis, which seems to thrive at Bermu- 
das better than almost anywhere else, forming domes six or 
eight feet in diameter—the animal matter is in comparatively 
small quantity, and covers the coral with what appears little 
more than a coating of grayish or yellow mucus. The Gor- 
gonie, the Bryozoa, and the Hydroid zoophytes are like the 
other more prominent weeds in the field, as abundant and as ir- 
regularly distributed, growing in the spaces between the clumps 
of the different kinds of coral. One form, J/dllepora, which 
has been latterly classed with the hydroids, but which would 
seem to be more nearly related to the lost order Anthozoa rugo- 
sa, represented by two species, JZ. aleicornis and ML. ramosa, is 
extremely abundant at Bermudas, where it acts in every way the 
part of a coral, forming massive additions to the reef of carbon- 
ate of lime abstracted from the sea. Beneath these large things 
there is usually a close felting of an undergrowth, consisting 
partly of sponges and smaller zoophytes, but chiefly of what are 
sometimes called lithophytes, sea-weeds of such genera as Co- 
rallina, Melobesia, and Nullipora, which, like corals, take car- 
bonate of lime from the sea-water and incorporate it with their 
tissues. 
All these things, living and dying, are constantly yielding a 
fine powder of lime, which sinks down and compacts in the 
spaces among their roots; and every breaker of the eternal surf 
grinds down more material and packs it into every hollow and 
crevice capable of receiving and retaining it. A great order of 
worms, including the genus Serpula, secrete carbonate of lime, 
and form thick and large calcareous tubes, or make galleries 
through the partially consolidated calcareous mud, and harden 
it and bind it together. So great a part do these worms play 
in the construction of the reefs at Bermudas, that General Nel- 
son, in an admirable paper on the geology of the islands, pub- 
