2i6 THE BIOLOGY OF THE SEA-SHORE 



particular, has led to interesting arrangements whereby 

 water may be drawn from the surface or filtered clear of 

 sand. One of the best examples of these is provided by 

 Corystes in which the antennae, when apposed, form a long 

 tube, down which, in consequence of the reversal of the 

 normal respiratory current, water is drawn into the gill- 

 chambers. The habit of burrowing also involves inte- 

 resting respiratory problems such as the effect of the 

 accumulation in the sand of decaying substances and of 

 the waste products of metabolism. 



Wave action has here been seen to involve yet another 

 source of danger to certain shore animals : that of asphyxia- 

 tion in consequence of the agitation of the sand and mud of 

 the sea-bottom. In Plymouth Sound, for instance, selective 

 mortality among the members of the local fauna was caused, 

 during a certain period, by an increased turbidity of the 

 water due to physical changes introduced by man. A 

 consequence of particular interest was that those crabs 

 tended to survive which varied in the direction of greater 

 efficiency in the methods of filtering the water required for 

 respiration. 



An extreme example of how turbidity of sea-water may 

 affect marine animals was provided by a rain of ash from 

 Vesuvius in April, 1906 (Lo Bianco, 1906-8). Here, also, 

 the mortality caused by the matter in suspension, among 

 the animals of Naples Bay, was selective, some forms 

 suffering only slight inconvenience, while others, such as 

 sea-urchins, were wiped out. The death of the sea-urchins 

 was due to clogging of the madreporite,and other forms which 

 succumbed in more or less analogous fashion to the 

 mechanical effects of the ash were Amphioxus and various 

 bivalve molluscs. The consequences of the catastrophe 

 continued to be felt for many years. 



