262 OCTOBER. 



tentacles are allowed to depend like spiders' webs, or 

 are suddenly drawn up into shrivelled puckers, become 

 mutually entangled and intertwisted, then slowly free 

 themselves, and hang down again. Sometimes the 

 motionless bell itself sinks very gradually, and the 

 tentacle-threads take the most elegant curves and arches 

 in their descent. 



The manner in which the strong pulsating move- 

 ments of the Medusae are performed depends on the 

 position and action of certain bands of muscular tissue. 

 Four of these radiate from the centre of the dome to 

 the margin. This course is not a straight but a curved 

 one. When, therefore, these bands are simultaneously 

 and forcibly contracted in length, they are drawn from 

 a curved into a straight line,, and the cavity, which was 

 bell- shaped, becomes more conical, and its capacity is 

 considerably diminished ; a portion of the water which 

 it before held is therefore driven out at the mouth, and 

 by its reaction forces the animal forward with a jerk 

 in the opposite direction. Besides these radiating 

 muscles, there are circular bands which pass round 

 the ' margin and the interior walls of the dome. These 

 by their contraction diminish the volume of the cavity, 

 and aid the action described above. 



The tiny Sarsia has but four tentacles, which spring 

 from as many equidistant points on the margin of the 



