THE ANIMALS OF THE MARINE AQUARIUM 129 



burrowing worms like Arenicola, Nerine and so on ; burrowing 

 sea-urchins like Echinocardium ; even burrowing sea-anemones 

 like Peachia may be found, but in the general case the natural 

 conditions of sand-burrowers are not easily imitated in an 

 aquarium, and one can hardly hope to keep them there for more 

 than a short time, and then under somewhat unnatural con- 

 ditions. Again, though these same sandy shores are sometimes, 

 after heavy gales, found strewn with interesting forms, these are 

 for the most part dead or moribund, never in the best condition 

 for introduction into the aquarium, though of course the zealot 

 will omit no opportunity of studying the habits of marine animals. 



The ideal collecting ground is furnished by a considerable 

 extent of rocks, interspersed with pools, and in collecting notice 

 should be taken of the haunts of the animals selected. The 

 most obvious peculiarity of the conditions of life on the shore is 

 the ebb and flow of the tide. When it ebbs a certain proportion 

 of the shore animals go with it, while another proportion lurk 

 beneath weed, under stones and in dark damp recesses, until its 

 return, both for safety and because if not water at least damp air 

 is necessary to their well-being. Now, as a general rule to 

 which, of course, there are exceptions success in the aquarium is 

 more apt to be attained with the forms which linger in the pools 

 than in those which habitually wander seawards with the ebbing 

 current. If you find in the pools little fish, for instance, which 

 are not reluctant to bury themselves in wet weed instead of 

 remaining in the water, you are more likely to keep these alive 

 in your aquarium than the strong swimmers who never voluntarily 

 leave the water. In general, success is more probable with the 

 relatively sluggish forms than with those which are strong enough 

 to swim against the currents, or so delicate and helpless that 

 they must float passively with it because they cannot resist its 

 action. The reason is that the latter two sets require a more 

 constant supply of oxygen than it is generally possible to give 

 them in the ordinary aquarium tank. 



After these preliminary hints we may run through a few 

 forms in each of the great classes, selecting those which may 

 be kept in the aquarium with more or less prospect of success. 





VOL. II. 9 



