80 VIGNETTES FUUM INVISIBLE LIFE. 



until the goal is reached ; or they will turn them- 

 selves over with a bound. Another method has 

 been observed : by hanging head downwards on 

 the surface, with the foot thrown out above, and 

 thus floating with the stream. 



There is very little of organisation in the Hydra ; 

 yet they are possessed of one extraordinary power 

 in their stinging organs. If one takes a Hydra and 

 places it under pressure, then with the microscope 

 will be seen a number of small oval capsules (which 

 the pressure has forced out on to the glass), with a 

 long and fine point projecting out from each, as in 

 the woodcut; and it is supposed that it is with 

 these that the prey of the Hydra is secured and 

 killed. It may be conjectured that these points 

 are coiled up within the capsule, and are used only 

 when wanted, when they spring out with force 

 enough to penetrate their victims. The sin- 

 gular effects of this impact have led to the con- 

 clusion that these capsules contain poisonous 

 matter, and this is apparently confirmed by some 

 chemical tests. A worm, which is so tenacious 

 of life that if cut in pieces each piece will live 

 a considerable time afterwards, is yet instantly 



