1889.1 Wa/ks Under the Sea by a Coral Strand. 953 
sides of this cup. They correspond to the tentacles, and with 
the latter increase in number with the age of the polyp according 
to definite laws. The animal then begins to reproduce asexually 
by division and budding, and the method and degree of com- 
pleteness with which this is carried out, determine the form of the 
coral stock. The fragile madrepores branch in the most intricate 
manner, while other forms are massive, the cups of individual 
polyps being closely crowded and united in a common base. In 
the brain corals the sides of the neighboring cups unite to form 
intricately winding valleys. 
The fan corals or alcyonaria (named for Alcyone, the daughter 
of Neptune) have invariably eight tentacles, and usually a horny in- 
stead of a calcareous skeleton. Under this head falls the Corallium 
ruhrum of the Mediterranean, which yields the red coral stone of 
jewelry, but it is exceptional as regards its hard skeleton. 
It quite as true of the corals as of the flowers of the field, " they 
toil not neither do they spin," and any metaphor of the poet which 
implies ' labor ' or ' skill ' in the polyp community such as we see 
i^i the construction of the honey-comb by the bees is rightly ob- 
jected to as being misleading, since it is false to nature. The 
white and porous limestone structure which we call " coral," or 
technically a corallum, is in fact the inorganic frameworks of the 
polyp colony, and it costs the coral animals just as much labor 
as it does us to make the bones in our bodies. 
Reef-building corals occupy a zone about 28° on either side of 
the equator and in both palaeozoic and recent times they have 
produced important changes on the earth's surface, building up 
islands in the sea and adding to the coasts of continents. They 
do not flourish below a depth of 15 — 20 fathoms, and are absent 
from the mouths of rivers, since they require the pure sea water. 
Once let the waves throw up a sand bar on the reef, and a new 
island is therewith born. A thousand and one objects attach 
themselves, and the constructive processes get the upper hand. 
The mangrove tree is an early visitor, and its peculiar methods of 
growth fit it admirably as a pioneer in the vegetation of the new 
island. The seeds of this plant develop in the calyx, before they 
fall from the tree, each sending out a curved cylindrical stalk 
