THE WEB OF LIFE 291 



it now insinuates its body into its host in a quiet leisurely 

 way. When the Holothurian is placed in water with 

 insufficient aeration, the fish conies out, and rises to the 

 surface, taking in gulps of air. 



Numerous small horse-mackerels (Carangidse) swim 

 about under the shelter of the umbrella of large jelly- 

 fishes, and other small fishes find safety among the very long 

 and hair-hke spines of the dark-coloured rook-urchin 

 (Diadema saxatile). Prof. Weber notes that as many as 

 ten specimens of a pelagic fish (Nomeus gronovii) may be 

 found in the shelter of the tentacles of the Portuguese 

 Man-of-War (Physalia). There is a fish called Amphiprion 

 hicinctus, which fives inside a large sea-anemone (Crambactis 

 arabica), and Prof. Plate has described Apogonichthys 

 stromhi, from the Bahamas, which spends at least part 

 of its time ia the mantle cavity of large specimens of 

 Strombus gigas. 



It must be confessed that the hermit-crab does not seem 

 to be always happy in its choice of a shelter. Prof. Chilton 

 tells how Eupagurus stewarti, which has a straight abdo- 

 men, inhabits tubular cavities within a MiUepore or a 

 calcareous Polyzoon. The cavities may be due, as Prof. 

 Benham suggests, to the decay of a branch of seaweed 

 around which the MiUepore or the Polyzoon grew. But 

 the point is that the calcareous shelter may be much larger 

 than the hermit-crab, and must be very heavy, if not too 

 heavy, to carry about. 



An intermediate state of afiairs is illustrated when two 

 animals share the same dwelhng without sharing food. 

 Thus the prairie-owl fives with the ' prairie-dog ' in North 

 America, and another species of owl with the Viscachas 

 in South America. Perhaps in the same category may be 



