ZOOLOGY. 345 



has been the necessity of frequently changing the salt water requisite 

 for their further existence. This has been overcome in the following 

 manner. In the course of the experiments, it became known that by 

 aerating the salt water by filtering or agitation, it became fitted for the 

 support of animal life. Here, then, a chance of success to an object 

 long desired seemed to present itself; and the enterprising Secretary 

 of the Zoological Society determined to make a trial on a small scale. 

 He began with the sea anemones and some of the more hardy shell- 

 fish, and succeeded most satisfactorily. AVhile, however, this experi- 

 ment was in progress, a fact of much greater importance became 

 known. It had been observed by vegetable physiologists that plants 

 purify a small quantity of water just as they purify the air, that is, by 

 taking up carbonic acid and giving out oxygen : and here was the 

 explanation of the fact of animals living for any length of time in a 

 limited quantity of water, provided there were plants enough to take 

 up the carbonic acid which the animals threw off, and supply the oxy- 

 gen which they needed. The question naturally arose, why should 

 not sea-weeds do the same for sea water as fresh water plants do for 

 fresh water ? The experiment was tried by the Secretaiy, and has 

 proved successful. By arranging sea plants and animals in a limited 

 quantity of sea water, he so maintained the balance of animal and 

 vegetable life, that for several months they required neither fresh 

 water nor any mechanical aeration. It is the adoption of this plan on 

 a large scale that constitutes the novelty of the Vivarium now opened 

 to the public in the Zoological Gardens. 



At the present there are six large tanks of glass containing various 

 forms of marine invertebrate animals and fish. These tanks have been 

 arranged in something like zoological order. The first contains a vari- 



cj ^j ^? 



ety of Crustaceans, crabs, lobsters, and shrimps. Here may be seen 

 in living activity species of these creatures only to be caught by the 

 dredge, and which have been only occasionally'seen when cast up on 

 our coasts or pinned down in our museums. 



In a second tank is a collection of Echinodermata. These creatures 

 are familiar in their common types the star-fish and the sea-egg. 



A third tank contains a collection of sea anemones, or animal flow- 

 ers. The more common, forms of these lowest members of the great 

 family of Polyps are scarcely unknown to the least curious visitors to 

 our sea coasts ; but it has fallen to the lot of few to see them to such 

 advantage as they now may here. In variety of color, they almost vie 

 with a bed of tulips ; and they will enable the observer to understand 

 something of the beauty which arrests the attention of the traveller in 

 the South Seas, where these creatures and their allied forms abound. 



In a fourth tank is a collection of British Mollusca. Those who 

 gather shells on the sea-shore will recognize many of their old acquain- 

 tances in this department, but no longer as uninhabited dwellings. 

 Each contains its proper tenant. In another tank, a highly interesting 

 group of mollusca the Xudibranchiate are to be seen. These have 

 no shells and are remarkable for their delicate coloring and for the 

 curious forms assumed by their gills or breathing organs, which being 



