62 MARCH. 



arrangement of the interior, and other points of value, 

 have indeed been progressively made ; whereby the prac- 

 tical availability of the invention for the purposes of 

 experimental natural history has been augmented ; but 

 some of us have found little difficulty, even from the 

 very first announcement of the discovery, in maintain- 

 ing the collections of sea- water, with their living plants 

 and animals, unchanged from year's end to year's end. 

 I may be perhaps excused for observing, that I have at 

 present in use a large tank, full of marine creatures, in 

 which the water has been unchanged for four years, and 

 on which I look with peculiar interest, because it w r as the 

 first tank ever made for private use. This very aquarium 

 has afforded, and still affords the opportunity for the 

 observation of many interesting details of the structure 

 and habits of the lower forms of animal life, details 

 which constitute the basis not only of my works on 

 marine natural history already published, but of the 

 present series of papers also. We collect the creatures, 

 indeed, abroad, and there gather up some broad facts of 

 interest concerning their modes of life ; but it is at 

 home, in the quiet of the study, with conveniences 

 and aids to examination, experiment, and record at 

 command, that they must be studied. The aquarium 

 becomes in fact an apparatus, whereby we bring a 

 portion of the sea, with its rocks, and weeds, and 



