A Brief History of a Marine Tank. 261 



and this cannot easily be renewed in the event of its becoming- 

 foul. The largest tank ever made, and the largest series of 

 tanks ever made, are but as drops as compared with the 

 ocean, and the physiological and chemical phenomena taking 

 place within them are on the same small scale as the tanks 

 themselves. For instance, in place of the rush of the tide 

 with its crest of foam and grinding of pebbles in a rock-pool, 

 giving life and energy and abundance of food to the creatures 

 that the pool shelters, in the tank there is of necessity a death- 

 like stillness. This stillness reduces the capacity of the water 

 for sustaining animal life, it is antagonistic to the generation 

 of oxygen within or its absorption from the atmosphere. The 

 algas that grow in rock- clefts and among littoral deposits are 

 fully exposed to solar light, and are sometimes laid bare for 

 hours to a burning sun. I know of many lovely meadows of 

 Ulva and Enteromorpha, but principally the former, which are 

 daily almost as dry at low tide as the hot sands above the 

 water-line. We dare not imitate this feature in tank manage- 

 ment. Sunshine makes our small pools opaque and viscid with 

 an extravagant growth of superfluous vegetation, and as to 

 laying the shoal dry daily it is out of the question, except it 

 may for some unhappy individual who has nothing else to do 

 than to pump or dip, and sell himself soul and body to a boxful 

 of worms and periwinkles. If we keep marine animals at all, 

 it must be by simpler methods than these. Lastly, to avoid 

 tediousness, the animals we imprison are imprisoned ; in other 

 words, they do not select the site for themselves as when free, 

 and with the immeasurable floor of the ocean for their play- 

 ground ; nor once consigned to the slate prison can they shift 

 their quarters, even if, as may be the case, those quarters are 

 not exactly to their liking. Seeing that in this brief view of 

 a few of the details of the case, there are many difficulties to 

 be encountered, it is a matter for gratulation and perhaps for 

 pride, that so much has been done to enlarge the boundaries 

 of our. knowledge of the life that abounds in the deep sea. 



Having fitted up and tended tanks innumerable, I always 

 found that the best " weeds" for ordinary purposes were Ulva 

 latissima and Enteromorpha com/press a. I have made some 

 practical notes on other forms of algse in the Booh of the 

 Aquarium, and have no intention now to repeat myself. I 

 found, moreover, that the best of all materials for rockwork 

 was mica-schist, because on this there soon occurred a spon- 

 taneous growth of microscopic algse a,nd confervee, which is 

 the best growth for a free generation of oxygen, and for 

 keeping the tank in good condition. But with the best 

 arrangements there was a certain amount of management 

 wanted, and the object of fitting up the tank, of which a 



