180 THE ELEMENTARY NERVOUS SYSTEM 



tal to the buried portion. The contraction of the stalk 

 on its long axis must be attributed, therefore, to the ac- 

 tion of its longitudinal muscle. 



When the distal end of a decapitated stalk is exam- 

 ined, a plug of large vacuolated cells is seen to protrude 

 from it. These cells, well known to the earlier students 

 of Corymorpha, fill the axial part of the polyp and serve 

 to a certain degree as a skeletal tissue. When the polyp 

 contracts longitudinally, they are crowded together 

 lengthwise and on relaxation they doubtless tend to re- 

 turn the stalk to its originally elongated shape. But this 

 operation is probably much facilitated by the action of 

 the circular muscle of the stalk, whose contraction would 

 crowd the mass of axial cells back to its elongated form 

 and thus restore the stalk to its original shape. Thus by 

 the alternate action of the longitudinal muscle and the 

 circular muscle on the mass of axial cells the contraction 

 and elongation of the stalk is accomplished. 



If live decapitated stalks of Corymorpha, are placed in 

 seawater containing magnesium sulphate or chloretone, 

 they soon become incapable of longitudinal contraction. 

 The stalks retain what would be called the elongated con- 

 dition. If one of these anesthetized stalks, particularly 

 one that has been treated with chloretone, is vigorously 

 prodded at a given spot with a blunt rod, though no longi- 

 tudinal contraction occurs, in the course of three-quar- 

 ters of a minute to a minute a constricted ring appears on 

 the stalk and remains there for from five to eight min- 

 utes. If the same experiment is tried with a stalk that 

 has not been anesthetized, the stalk immediately con- 

 tracts lengthwise but elongates soon afterwards, during 

 which a ring of constriction appears and may remain evi- 

 dent for as much as ten minutes. 



