SPECIAL PROBLEMS OF SHORE LIFE 65 



of the tide (Bohn, 1901). A pretty way of solving this 

 difficulty is seen in Cirratulus. In this worm one of the 

 anterior segments bears two thick clusters of long, very 

 vascular filaments. In the natural habitat all that is seen 

 of the worm is this cluster of deUcate rosy processes gently 

 waving in the water of a pool. When Cirratulus burrows, 

 these filaments, which are exceedingly elastic, are left pro- 

 truding in the waters of a pool and serve to aerate the blood 

 while the worm is finding its food in the decaying mud below. 

 In this way, safe from drought, enemies, and asphyxiation, 

 Cirratulus is able to live undisturbed (Flattely, 1916). 



Methods of resisting Drowning employed by Shore Forms 

 breathing Atmospheric Oxygen. — So far, the problems we 

 have been discussing are those confronting the essentially 

 marine animals which form the mass of the shore population. 

 There is, however, another small group of animals which, 

 though the near relatives of typically terrestrial forms and 

 quite incapable of breathing dissolved oxygen, form an 

 undoubted part of the shore fauna. This group is com- 

 posed of forms, mostly insects and arachnids, which are 

 making a tentative return to the habitat which their distant 

 ancestors may, perhaps, be said to have deserted. The 

 difficulty offered to these forms by the tides is the exact 

 opposite of the one confronting the marine types. It is low 

 tide which is the period of activity for these forms, the 

 problem for them being how to subsist during the periods of 

 high water. We may mention here the fact that the littoral 

 mite Gamasus [Halolcelaps] glabriusculus has been shown by 

 King (1913) to be capable of enduring complete immersion for 

 at least forty-eight hours. During this time the mite is quite 

 inactive, but resists asphyxia by the aid of the air imprisoned 

 in its breathing tubes. Marine insects are usually Uberally 

 covered with hairs which serve to imprison bubbles of air. 



THE PROBLEM OF WAVE-IMPACT 



As the tide rises and falls successive areas of the shore 

 are pounded by the breaking waves, often with tremendous 



F 



