402 THE AMERICAN NATURALIST [Vol. XL 



bending back and forth singly or collectively. The manubrium 

 {mah.) is ordinarily motionless, but may shorten or lengthen and, 

 when stimulated, is capable of bending even to such an extent that 



the mouth is brought below the bases of the |)ro\-inial tentacles. 

 The whole hydranth may l)e moved by the bending of the stalk, 

 but this action is not of frequent occurrence and it is apparently 

 not called forth in rcs]:)onse to direct stinuilation. 



When a proximal tentacle is touched with a needle or pinched, 

 it bends toward the manubrium. The strength of the stimulus 

 influences the res})onse. If the stimulus is weak, there may be no 



up together and press against the niiiiiuliriiim. If tlic maiuibrium 

 or the distal tentacles are stimulatc.l in a .iiiiilnr manner, the for- 



