DECEMBER 



119 



the animals once a week a very little scraped beef, but 

 great care must be exercised to remove the undevoured 

 food. 



With a sponge, keep the outside and inside of the 

 aquarium clean. The water in evaporating is apt to 

 leave an ugly white line, which, however, may easily be 

 removed. The water should be replenished from time 

 to time, pouring it over the hand, as before, to break the 

 force of its descent. 



If the animals die, it is because they were diseased in 

 the first place, or because the aquarium gets too little 

 light, or because food is allowed to decay, or because the 

 room is kept too hot for either fish or children. If the 

 water becomes quickly green, it is because the aquarium 

 receives too much light. 



Lateral 

 Lime . 



5TFIL-, 



Mouth 



Fish. 



Facts : 



The external anatomy of the fish is probably sufficiently- 

 indicated by the cut. The arm and leg fins, so named 

 from their homology to our own legs and arms, are paired. 

 All of the other fiiis are single. In some of the lower 

 fish and in some embryos, the back, tail, and anal fins are 



