THE STUDY OF SHORE ANIMALS. 21 



with a spring tide the water may drop a vertical height of 

 up to forty feet; so that it is obvious that unless the moisture- 

 loving animals can allow for the periodic movement of the 

 waters, they must be very liable to elimination either by 

 direct drying up, or by exposure to the keen sight of the 

 birds who follow the receding waves. So far as we know, 

 the tide has always ebbed and flowed, wherefore the shore 

 animals have had time to learn their lesson. The result 

 is that sedentary animals like sea-anemones, sea-squirts, 

 Alcyonarians, sea-firs, and the like establish themselves 

 only under overhanging rocks or in deep crevices where, 

 even when the waters retreat, there is a grateful coolness 

 and moisture, and a refuge from keen eyes. Sluggish forms, 

 like many Annelids, the ribbon- worms, the starfishes and 

 brittle-stars, sea-slugs, and many more which are equally 

 unable to follow the water, and equally unwilling to be 

 deprived of moisture creep into similar situations or under 

 stones and weed, to pass their time of waiting; and there 

 are left exposed a few hardy forms only, with some special 

 means of minimising the risk of drying up. Finally, at every 

 tide, but more especially at the springs, certain active forms 

 are prevented by untoward circumstances from escaping with 

 the ebbing water, and are held prisoners until it comes again. 



FIG. 7. Lump-sucker (Cycloptenis lumpus). After Day. 



Among such are many fish, lump- suckers, gobies, stickle- 

 backs, sea-scorpions, and others; at certain seasons of the 

 year the large cuttles, various Crustacea, and many other 

 curious creatures. If these facts are borne in mind, it will 

 be obvious that rocks are most likely to yield a rich harvest 



