PKBPAEING THE TANK. 37 



bear as low a temperature as our native species from rea- 

 sons that I have mentioned before. However, I have had 

 minnows living* beneath a cake of ice an inch thick in my 

 tank. Of course, if we allow the water to freeze, we shall 

 •endanger the bursting of the vessel from the expansion that 

 water always undergoes when passing from the liquid to 

 the solid state. Mr. Ilibbcrd, in his useful little book on 

 the Aquarium, mentions that he finds that " a northerly 

 aspect will do very well, say from May to October ; but 

 during the winter months a tank in such a position would 

 be feeble and want watching." A good plan is to place a 

 fresh-water tank close to the window, and during most of 

 the year leave it open ; this, of course, cannot be done dur- 

 ing the winter, but the sash can be lifted for about an hour 

 a day, and you will find that the fish thrive the better for 

 it. It is mentioned in most of the books on the subject, 

 that marine Aquaria do not- recpiire much light ; and Mr. 

 Ilibbcrd recommends the placing of them behind fresh-water 

 tanks, so that they receive little, if any, light through the 

 sides. This may be advantageous for the deeper water spe- 

 cies, but, in general, where I have used Ulva, Enteromor- 

 yha, GrinneUia and Cladaphora, with hermit-crabs, minnows 

 aud Anemones, I have found that one or two hours a day 

 of bright sunlight is highly serviceable to the growth of the 

 plants, and exhilarates the Anemones wonderfully, making 

 them expand and exhibit their beauties in a fiue maimer. 

 In the sea, it is true, that the light falls through the 

 surface of the water, and on this principle is Mr. AYarring- 

 toirs tank contrived, and in it sea species thrive wonder- 

 fully. This fact should also hold true in regard to fresh- 



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