148 THIl MICROSCOPE!. Oct. 



power they are seen to be covered with a series of little 

 points. It is these which contain the poison sacs. They 

 consist of a depression containing a bladder full of 

 liquid haline, in which is plunged a spiral thread ter- 

 minated at the base by an enlarged trident, the hooks of 

 which turn back (fig. 5, 6). At the least touch, the spring 

 unrolls itself and the fllamant, impregnated with the 

 poison, penetrates the body of the imprudent beast, 

 which thus loses his power of voluntary movement. The 

 three hooks at the end of the sac cannot penetrate into 

 the body of the victim since they are at the base of the 

 thread and not at its extremity (fig. 5), as has been er- 

 roneously stated. Besides, if they penetrated at the 

 same time as the needle the animal would lose them be- 

 cause he would not be able to withdraw them. It is 

 true there would still be enough left, for his tentacles 

 are covered with them. 



The hydra have many curious peculiarities. They 

 walk like the Geometrid caterpillar, using their mouth 

 as a cupping glass as opposed to that of the foot. They 

 take a step upon the head and draw up the foot to the 

 neck and so continue. They run as a gymnast, who 

 turns a somersault upon his hands to come back upon his 

 feet again on the other side. They have no eyes • yet 

 they seek the light the same as plants and infusoria. 



They probably feel light as we feel heat. They digest 

 with their skin as with their digestive mucous. This is 

 proved by turning them inside out as we do the finger of 

 a glove. A hydra which has been turned inside out can 

 be made to sw^allow an ordinary hydra or vice versa, and 

 two hydra can be joined body to body so as to make only 

 one, armed with a double row of tentacles. They can 

 be made to grow again or can be made to grow from a 

 piece. 



I. To TURN A HYDRA INSIDE OUT. There are several 

 ways of doing this. A practical way is to take advant- 



