ACALEPH^B. 207 



towards its mouth, swallows it. Trembley amused himself by feeding 

 the Hydra, while he observed the manner in which it devoured its prey. 

 " When its arms were extended, I have put into the water a wood- 

 louse or a small worm. As soon as the woodlouse feels itself a prisoner 

 it struggles violently, swimming about, and drawing the arm which 

 holds it from side to side ; but, however delicate it may appear, the 

 arm of the polyp is capable of considerable resistance; it is now 

 gradually drawn in, and other arms come to its assistance, while the 

 polyp itself approaches its prey ; presently the woodlouse finds itself 

 engaged with all the arms, which, by curving and contracting, 

 gradually but inevitably approach the mouth, in which it is soon 

 engulfed." Fredol also notices a singular fact. " The small worms, 

 even when swallowed by the polyp," he says, "frequently try to 

 escape ; but the ravisher retains them by plunging one of its arms 

 into the digestive cavity ! What an admirable contrivance, by which 

 the worms are digested while the arm is respected !" 



The food of the fresh-water Hydra influences the colour of their 

 bodies in consequence of the thinness and transparency of their 

 tissues; so that the reddish matter of the woodlouse renders them 

 red, while other food renders them black or green, according to its 

 prevailing colour ! 



The multiplication of these creatures takes place in three different 

 ways : 1. By eggs. 2. By buds, after the manner 'of vegetables. 

 3. By separation, in which an individual may be cut into two or many 

 segments, each reproducing an individual. 



We shall only say a few words on the first mode of reproduction. 

 The eggs, according to Ehrenberg, come to maturity in the H. viridis 

 at the base of the feet, where the visceral cavity terminates. They 

 are carried during seven or eight days, and determine by their fall the 

 death of the animal. When the Hydra has laid its eggs, according to 

 M. Laurent, it gradually lowers itself until it covers them with half 

 its body, which, spreading out and getting proportionably thin, passes 

 into the condition of a horny substance, that glues the eggs disposed in 

 a circle round the body to plants and other foreign substances. She 

 ends her career by dying in the midst of her ova. 



Trembley has studied with great care the mode of reproduction by 

 budding a process which seems to prevail in the summer months. 

 The buds which are to form the young polyp appear on the surface 



