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- 

 salid) 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 medusae 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 



