150 THE MICROSCOPE. Oct. 



ing the skin to the skin or the mucous to the mucous. 

 But one cannot unite the skin of one to the mucous of 

 another, for when a small hydra is swallowed by a large 

 one, the larger one soon rejects it, or if it happens that the 

 small one is retained the large one finally digests it. 

 They cannot be made to grow together. 



To unite the hydra, mucous to mucous, turn as the 

 finger of a glove the polype which is to be swallowed, 

 and cause it to be taken by the second one by pressing 

 it into the digestive cavity with a silver wire. The two 

 mucous membranes are then in immediate contact. In a 

 few days the w'alls of their bodies have grown into one, 

 and it is only a single polyp that digests with what was 

 the skin of the smaller animal, the only difference 

 being that its body is thicker than in the normal state, 

 for it is composed of a double row of tissues and that it 

 has a double row of tentacles. 



To make them unite skin to skin, the one which is to 

 swallow the other should be turned inside out and by 

 the aid of a needle pressed one inside the other. 



When one attempts to unite the skin to the membrane 

 and holds them (the little one smallowed by the larger 

 one) together with a needle inserted transversly ; it hap- 

 pens that they do not grow together but the exterior 

 hydra allows himself to be torn by the needle the whole 

 length of his body, while the smaller one remains whole 

 but taking the needle with him. The larger one grows 

 together again. 



III. To DIVIDE A HYDRA INTO SEVERAL. When a hydra 

 is divided into two parts lengthwise, in twenty-four 

 hours the parts will have healed leaving two polyps, each 

 a little smaller around than at first and having one-half 

 the number of tentacles of the original. When a hydra 

 is cut in two transversely it takes two days for one part 

 to form a new foot and the other a new crown of ten- 

 tacles. When a hydra is cut into three pieces with the 



