2 LIFE BY THE SEASHORE. 



nowadays given to very many people for at least a few 

 weeks in every year, and even in this brief time it is 

 possible to acquire not a little knowledge of the ways and 

 structure of the common shore animals. 



We shall not at present seek strictly to define the mean- 

 ing of the word "shore," but in beginning a preliminary 

 study of the conditions of shore life, may conveniently start 

 from that commonplace of observation, which shows that all 

 parts of the shore area are not equally productive. It is 

 true that wherever the ebbing tide leaves bare long stretches 

 of sand, there will be found some of the inhabitants of the 

 littoral waters, living or dead, according to the force of 

 the waves which have torn them from their rocky homes ; 

 but we all know that to find these animals in their natural 

 conditions we must forsake the sandy beach for the weed- 

 covered rocks. In order to understand why it is that the 

 majority of shore animals live in the vicinity of rocks, let us 

 watch what happens when some change of current uncovers 

 a ridge of rock hitherto concealed by the sand. We find 

 that the first organisms to appear are usually Algae of various 

 kinds, the coarser kinds being often the most obvious at 

 first. Then come acorn-shells and vegetable-eating Molluscs, 

 and as these thrive and multiply they are followed by car- 

 nivorous whelks, buckies, and starfishes. As the weeds 

 grow, crabs and other Crustaceans make their appearance, 

 and the new settlement thrives apace until it contains most 

 of the animals inhabiting the parent area. How the 

 animals reach the new area is a question to which we 

 shall return later; our special concern now is what deter- 

 mines the gradual colonisation, and why does it only occur 

 where there is a solid substratum of some kind? The 

 answer is simple; it is essentially a question of food, and 

 the food upon which shore animals depend is most abundant 

 in the vicinity of rocks. 



Let us for a moment consider generally the food-supplies 

 of marine animals. The simplest case is probably that of 

 the pelagic animals, or those animals which live in the open 

 waters of the sea. These all depend ultimately either upon 

 the microscopic plants with which the water is filled, or 

 upon microscopic animals which because they contain green 

 colouring matter are able to feed like plants. The depend- 



