62 THE WONDER OF LIFE 



We often see ' nutritive chains ' the worm feeding on 

 debris, the crab feeding on the worm, the shore-fish swallow- 

 ing the crab, the herring gull with a swoop lifting the fish 

 from near the surface of the water, the skua gull chivying 

 the herring gull and forcing it to relinquish its booty. 

 There are hundreds of similar concatenations. 



There is struggle for foothold, struggle for food, and 

 struggle against dislodgment ; and it takes every form 

 from a literal struggle for subsistence to a competition 

 for luxuries, from a life and death combat to a rivalry 

 of wits. The oyster-catcher tries to knock the limpet off 

 the rock with a dexterous stroke of its strong bill, the limpet 

 tries to hold fast ; the carnivorous sea-slug sometimes 

 secreting dilute sulphuric acid from its mouth tries to 

 bore through the back of a starfish which may succeed in 

 dislodging its enemy by creeping under a low shelf of rock ; 

 the hermit-crab seizes a worm, the worm breaks into two, 

 and the hermit-crab falls in among the tentacles of a large 

 sea-anemone. In a thousand forms there is that reacting 

 against difficulties and limitations which is the essence of 

 the struggle for existence. 



In illustration of weapons in more detail, let us take the 

 case of the sea-urchin. Among the large spines on its 

 test there are minute ones (pedicellariae) with three snap- 

 ping blades. They suggest three-bladed shears on the end of 

 a long flexible stalk. Some of them help to grapple food- 

 particles, some keep the test clean, and others, as Prouho 

 and von Uexkiill showed, give poisonous bites. On the 

 dorsal surface of the beautiful golden-yellow heart-urchin, 

 Echinocardium flavescens, there are many of these poisonous 

 * gemmiform pedicellarise ' which have been observed to 

 work very effectively. Grandolfi Hornyold put a small 



