THE GENERAL CHARACTERISTICS OF SHORE ANIMALS. 11 



when they are trapped in some rock pool by the ebbing 

 waters. 



The above brief account of the way in which animals 

 protect themselves against the dangers of their physical 

 environment may serve as an outline which your experience 

 in actual collecting will later enable you to fill up. We 

 may now look for a little at the ways in which the shore 

 animals protect themselves from their organic foes. In 

 some cases, as we have already seen, the same artifice which 

 protects an animal from the one set of dangers protects it 

 from the other. The fisherman's lob-worm (see Fig. 10, 

 p. 30) is greatly relished by very many fish ; we can hardly 

 doubt, therefore, that it is, in an ordinary way, protected 

 against these by its burrowing habit. Most tube-worms 

 vanish into their tubes instantly at the least alarm, often 

 merely at a shadow. It is reasonable to conclude that the 

 tube affords a natural protection. It is not very uncommon 

 on the shore to find mutilated whelks, which have apparently 

 had their anterior region bitten off by fish before they had 

 time to withdraw into the shell ; a fact which again suggests 

 the protective value of the shell. Facts of this kind might 

 be multiplied indefinitely, but the protective value of hard 

 shells is in the general case sufficiently obvious, and we may 

 pass on to less familiar means of defence. 



Many shore animals seem to be protected by their 

 weapons, whether of offence or defence, or by some un- 

 pleasant attribute. Thus the great pincers of crabs and 

 lobsters make them dangerous adversaries ; jelly-fish and 

 sea-anemones are protected by their stinging-cells; sponges 

 are often full of sharp spicules ; many worms have an 

 elaborate armature of bristles; and so on. The power of 

 self-mutilation, or autotomy, is also widely spread among 

 shore animals, and must often assist their escape. Most of 

 the shore crabs, if seized by a limb, will throw off the limb 

 and escape. Brittle-stars break their rays at the slightest 

 touch, and the separated portion keeps up active movements 

 for some time. Not a few "worms" throw off gills or 

 tentacles or other portions of the body when molested. In 

 this case the separated organs move about even more actively 

 than when attached, and doubtless distract the attention of 

 the enemy. In all cases where autotomy is practised, the 



