174 ANIMAL LIFE 
and polyps are always found growing in close association, 
though what the mutual advantage of this association is 
has not yet been found out. 
Among the coral reefs near Thursday Island (between 
New Guinea and Australia) there lives an enormous kind 
of sea-anemone or polyp. Individuals of this great polyp 
measure two feet across the disk when fully expanded. 
In the interior, the stomach cavity, which communicates 
freely with the outside by means of the large mouth open- 
ing at the free end of the polyp, there may often be found 
a small fish (Amphiprion percula). That this fish is pur- 
posely in the gastral cavity of the polyp is proved by the 
fact that when it is dislodged it invariably returns to its 
singular lodging-place. The fish is brightly colored, being 
of a brilliant vermilion hue with three broad white cross 
bands. The discoverer of this peculiar habit suggests that 
there are mutual benefits to fish and polyp from this habit. 
“The fish being conspicuous, is liable to attacks, which it 
escapes by a rapid retreat into the sea-anemone; its enemies 
in hot pursuit blunder against the outspread tentacles of 
the anemone and are at once narcotized by the ‘thread 
cells’ shot out in innumerable showers from the tentacles, 
and afterward drawn into the stomach of the anemone and 
digested.” 
Small fish of the genus Nomeus may often be found 
accompanying the beautiful Portuguese man-of-war (Phy- 
salia) as it sails slowly about on the ocean’s surface (Fig. 
104). These little fish lurk underneath the float and 
among the various hanging thread-like parts of the Phy- 
salia, which are provided with stinging cells. The fish are 
protected from their enemies by their proximity to these 
stinging threads, but of’ what advantage to the man-of- 
war their presence is is not understood. Similarly, several 
kinds of meduse are known to harbor or to be accompanied 
by young or small adult fishes. 
In the nests of the various species of ants and termites 
