1895 THE MICROSCOPE. 149 



age of the peculiarity which these animals have of dilat- 

 ing themselves when they have swallowed a voluminous 

 prey. Gfive them a bait like those employed by fisher- 

 men. This may be the larvse of the diptera, Chironomus 

 plumose. The hydra dilates itself to swallow. Profiting 

 by this movement, pierce his body from behind toward 

 the front with a thread of stiff silver or a steel wire such 

 as is sometimes found in a box with syringes and used to 

 clear the injecting needle. The hydra struggles and 

 throws itself up suddenly into its normal condition ; bat 

 try again with patience and at length he will be fatigued. 

 Hold with a pair of forceps the upturned part and the 

 animal will finally allow himself to be turned. At the 

 end of two days, or even less time, the hydra is hungry 

 and commences to eat in his new position, but still trying 

 to return in part to his former position. At first he di- 

 gests with the part of the stomach which he has drawn 

 inside, but soon he digests completely by the aid of his 

 skin, this having become a digestive mucous. Some- 

 times he grows together in the position at first taken 

 and continues the live thus, although somewhat short- 

 ened in length. Care should be taken in the first few 

 days to keep him in position by a needle, which prevents 

 him from returning to his normal position by pressing 

 from the interior toward the outside to prevent his draw- 

 ing himself into himself. 



The hydra can make a new mouth if for any reason 

 the old one is destroyed. This happens when the 

 estosarc is held against itself. It forms cicatricial 

 shrinking which finally obliterates the exterior orifice. 

 A new mouth then forms underneath the strangulation. 

 The anterior part may dilate itself either wholly or in 

 part, the result of which is a new mouth, lateral in the 

 latter case, terminal in the former. 



II. To UNITE TWO HYDRA INTO ONE. This operation 

 can be performed in two different ways, either by unit- 



