THE MOVEMENTS OF SHORE ANIMALS 153 



capable of swimming as well as crawling or burrowing. 

 Moreover, the varied nature of the bottom and the topo- 

 graphical position of the shore at the junction of land, air, 

 and water mean that among animals living on or frequenting 

 the littoral practically every conceivable means of locomotion 

 can be studied. 



The bodies of freely-moving animals and the hulls of 

 moving ships, etc., provide a convenient means of transport 

 for sedentary forms, and it is fully utilised by them. 

 Whether or not a particular larva of one of these sedentary 

 animals will settle upon a moving or upon a stationary object 

 would seem to be, however, almost certainly a matter of 

 pure chance. And yet there must be more in it than this, 

 for how have barnacles, for instance, acquired the resistance 

 to changes of salinity, temperature, etc., which enables them 

 to cling to a ship during the whole of a long voyage ? 



As some of the most characteristic types of displacement 

 we may enumerate the following : clambering, gliding, 

 swimming, burrowing, jumping, gliding on or hanging from 

 the surface film. Before entering upon a detailed discussion 

 of movement under these headings it will be profitable to 

 notice Gamble's (1908) interesting treatment of this subject, 

 in which he asks us to imagine a man in a boat provided with 

 oars and a boathook. The methods of progression possible 

 to this man are four, and they are analogous to four important 

 methods of movement among animals. They are : by 

 punting with one of the oars against the bottom, comparable 

 with the way in which many animals use their legs or similar 

 appendages ; by hauling against obstacles on the banks 

 just as burrowing animals (worms, Crustacea, and insects) 

 use hooks and claws to cling to the sides of their burrows ; 

 by sculling over the stern exactly as a fish uses its tail ; 

 and, finally, by rowing with a pair of oars, which is not 

 unlike the way in which insects and birds use their wings, 

 though, in the latter case, in order for the analogy to be 

 accurate we must picture the man as rowing with his face 

 towards the bows. 



Clambering. — Probably the animals showing some form 



