946 The American Naturalist. [November, 
ing sound it makes when taken from the water. Its general 
shape is that of a sun fish or bream. It is jet black, excepting the 
head and tail, which look as if they had been dipped in a golden- 
yellow dye. 
The brain corals {Diploria cerebrifortnis) already referred to, 
whose rounded surfaces are stamped with those peculiar, intricate 
patterns, take a high rank among reef-building polyps. They 
form masses from a few inches to several feet in diameter, or cover 
the bottom with large convoluted plates {Meandrina) These 
help largely in building up the " coral-heads," the highest points 
on a growing reef, where the word is synonymous with danger- 
ous rocks. A dozen different species may contribute to the 
growth of the head. Sponges and gorgonias attach themselves. 
You may see the bright rosette of a sea-anemone fastened to a 
stone, or detect the long " feelers " of the spiny lobster project- 
ing from some niche in the wall. Boring sea-urchins, mollusks 
and barnacles perforate the living stones and thus assist the 
destructive action of the waves. This explains the detached frag- 
ments of coral which we see strewn everywhere over a reef They 
fall an easy pray to the waves, and are slowly pounded into fine 
coral sand like that of the beach. This beach-sand is then end- 
lessly rocked and shifted about, mixed with pieces of coral, conch 
shells, and with the bones or stony remains of countless marine 
organisms which inhabit the neighboring sea, until the whole is 
sometimes cemented into compact sand-stone, the ultimate build- 
ing material of reef or island. By thus continually extracting 
matter from the sea water, and yielding it up in the form of solid 
particles of carbonate of lime, the insignificant polyp contributes 
to the growth of continents. 
The delicate madrepores {Madrepora arbuscidd) resemble deer's 
anders or the forms of some branching shrubs, which the least 
blow shivers in pieces. In the water they have a light lavender 
hue, but bleach to snowy whiteness in the sun. The " propeller 
coral," as it is called by the natives, resembles clusters of brown 
leaves. In some places the bottom is fairly peppered with small 
coralline masses, the size of paper weights, their surface deeply 
■ * 1 with vermiform characters, well named " chenille-stones" 
