downing] 



AN AQUARIUM IN A TUMBLER 



321 



for twenty-four to forty- 

 eight hours, then if you 

 have been successful you 

 will find the little animals 

 attached to the sides of 

 the jar, to the water 

 plants, or the surface film 

 of the water. 



The animal is hard to 

 see at first so that you 

 may think that you have 

 been totally unsuccessful, 

 but as you look more care- 

 fully you will see the 

 hydra abundantly. It 

 is a tiny cylindrical sack 

 attached by a slight en- 

 largement at one end, 

 called the foot. It bears 

 a circle of tentacles, 

 usually six, at the other 

 end, and in the midst of 

 these tentacles is the 

 mouth. Usually the 

 animal hangs mouth 

 down with its tentacles 

 floating in the water, 

 ready to capture swim- 

 ming animals that make 

 up its food. If the animal is desired for study in the school room 

 it is a good scheme to have each pupil provided with a tumbler. 

 In these put a little spray of the water plant that has been 

 brought in from the pond or such a plant as caboniathatis sup- 

 plied by dealers in gold fish. For that matter no plant is neces- 

 sary if the hydra is to be kept under observation for a short time 

 only, for they will live in the tumbler of water for several weeks 

 without the presence of the plant. A medicine dropper may be 

 used to transfer the animal from the larger jar to the tumbler. 

 Pick the animal up if it is on the surface film by simply drawing 

 the water into the pipette, the point of which is close to the 



£-.r^, 



Hydra bearing a bud. 



Nettle cells or nematocyst, before and after discharge. 

 The animal is pendant from bit of plant. 



