23 
regulated according to the season and the hour of the day. Direct 
sunshine should never fall on the aquarium, but there must be 
daily a sufficient amount of bright light upon it to stimulate the 
vegetation, and to cause the evolution of oxygen, which will be 
seen as bubbles of silver rising to the surface. In excessively hot 
weather the amount of light must be lessened, and the temperature 
of the tank kept down by covering it with wet cloths, and counter- 
acted by frequent aeration with the syringe ; and, if necessary, by 
drawing off a quantity of water at night and returning it in the 
morning. This last remedy lowers the depth of water for some 
hours—thus imitating the fall of the tide, and thereby assisting 
the oxygenation of the water left in the aquarium—while addi- 
tional coolness and freshness are imparted by the restoration of the 
remainder on the following morning. On the other hand, in very 
cold weather, it may be necessary to cover the tank. with thick 
carpet, the better to preserve an equable temperature. 
The importance of thus regulating the temperature, and pre- 
venting, if possible, any wide fluctuations, will be evident when it 
is considered that, while the atmospheric temperature of England 
is said to vary from about 20° to 90°, that of the sea ranges only 
from about 40° to 65°, and it is within these limits that the 
temperature of the aquarium should, theoretically, be kept. 
Practically, this is impossible with private aquaria, but every effort 
must be made to counteract the effects of excessive light and heat. 
* * * The best way of introducing vegetation into a new 
aquarium, is to procure from a shore-pool some stones covered 
with young plants of Ulva or Enteromorpha. A few older plants 
of the same species may also be introduced. These will flourish 
without difficulty, and give off spores which will, in their turn, 
grow up into healthy plants. There will, in due time, appear 
upon the stones and sides of the tank a confervoid growth, varying 
in colour with the season of the year, which may be encouraged 
within proper limits. The ulva, enteromorpha, and confervoid 
alge are the best producers of oxygen, and the most easily 
cultivated. Some other more ornamental plants may be introduced 
for effect if they can be obtained young and healthy, and well- 
rooted. Of red sea-weeds, the bestare G'riffithsia setacea, Corallina 
officinalis ; Callithamnion, and Chondrus crispus. Of green sea- 
weeds, the most suitable, in addition to Ulva and Enteromorpha, 
are Cladophora rupestris and Bryopsis plumosa. But all these orna- 
mental alge must be watched, and on showing symptoms of decay 
should be at once removed. The bottom of the tank (between the 
glass and the lower portion of the sloping platform) should have a 
depth of about an inch and a half of fine shingle. When the 
rockwork is arranged, some hollows should be left, which may be 
filled up, in some cases with shingle, and in others with sea-sand. 
These will be useful if Sabelle, Terebelle, and other annelids are 
