Harper, Reactions of Perichceta. 571 



These movements may be classified as follows : 



(a) Retraction of the head or tail. 



(&) A sharp recoil of the head often accompanied by a slight 

 recoil of the tail. There may be several successive retractions. 



(c) With stronger stimuli the middle becomes involved in the 

 shrinking and there is an increasing tendency to a rapid succession 

 of movements. These tempt one to use an illustration which may 

 call attention to mechanical features of the case. If one pushes 

 together the ends of a cylindrical coil of wire, unless perfect equality 

 of pressure is maintained the coil will spring to one side. In an 

 elongated soft bodied animal mechanical features of this sort are 

 present in the contraction of the longitudinal muscles. Squirming 

 movements are produced in regard to which one cannot always dis- 

 tinguish whether they are due to unilateral contractions, or to the mere 

 mechanical inability to contract the body in a straight line. But 

 there is no uncertainty in respect to the strongest form of shrinking 

 movements that they are due to rapidly alternating contractions of 

 opposite muscle bands. When partly stupefied in a solution of 

 chloretone the characteristic springing movements are given when 

 more chloretone is added, and the movement thus slowed down con- 

 sists of throwing the body into a coil, first to one side and then to 

 the other. The worms jump about in lively fashion when handled 

 and they may do the same when uncovered from their burrows. 

 They may jump in the same direction for a foot or so, but this 

 appears to be the result of chance and perhaps of momentum acquired 

 rather than of definitely directed movements. The leaping can 

 hardly be called a form of locomotion, though it involves some trans- 

 latory movement. 



From this account of the shrinking movements it appears that they 

 range from mere retraction of the ends to a rapid succession of alter- 

 nating movements, but all involve the longitudinal muscles alone, and 

 are characterized by their suddenness and the action of the body, 

 or its active portion, as a whole instead of by waves of contraction 

 as in locomotion. For description the terms retraction, squirming 

 and leaping may be employed; but it is manifest that these move- 

 ments make a continuous series with infinitesimal gradations not 

 susceptible of exact description without the aid of a kinematograph. 



