lyo AQUATIC MICROSCOPY FOR BEGINNERS. . 



Stomach of each becomes complete. A polype has 

 been cut lengthwise at seven in the morning, and in 

 eight hours afterwards each part has devoured a worm 

 as long as itself." Trembley also sliced them across, 

 and found that each piece developed a cluster of ten- 

 tacles, and he finally turned them inside out, and in a 

 few days the maltreated creature swallowed food, al- 

 though its old skin was now lining, its stomach, and 

 its old stomach-membrane had now become its skin. 

 This, at least, is Trembley's account. More recent 

 experimenters, however, have doubted the correctness 

 of this explanation, preferring to believe that while 

 Trembley was absent or a little absent-minded the 

 everted Hydra quietly turned itself right side out, and 

 so deceived its tormentor. 



There is a peculiar parasitic Infusorium (Fig. 132) 

 often seen in considerable numbers gliding rapidly 

 over the body and arms of the Hydra, especially of 

 H. viridis. They do not seem to be objec- 

 tionable guests, as the Hydra never appears 

 to notice them. It is said that they infest 

 sick or weakly victims only, but that is not 

 according to the writer's experience, if the 

 condition of the Hydra may be judged by 

 appearance, activity, and appetite. Several 

 Fig. 132.— of these parasites are shown on a portion of 

 pedTcu°iu'^ a tentacle in Fig. 132. Each is shaped like 

 Hydrl.° a short dice-box, with a circle of fine cilia at 

 each end, but none on the rest of the body. 

 It glides along' rapidly on the ends of the dice-box, 

 running out to the tips of the tentacles and skirting 

 fearlessly around the edges of the mouth. It is the 

 TrichoMna pediculus. 



