^yo journal of Comparative Neurology and Psychology. 



worm and the ends initiate the righting movements, making the 

 animal to roll over and over. Waves of contraction of the circular 

 muscles pass over the middle but are blocked at the ends which 

 remain passive as to extension, but continue to perform the right- 

 ing movements seemingly in response to the pull exerted upon them 

 by the middle. In addition to the pull there is some mechanical 

 twisting of the middle of the body in its extension to one side and 

 it may be this that stimulates the ends to execute the righting move- 

 ments. It appears j)i'obable also that the circlets of setae on each 

 segment, which are a family characteristic of the Perichsetidse, may 

 be functionally correlated with the rolling movement, helping the 

 maneuver by their action as hold-fasts. This is however a matter 

 of inference. The essential features are the activity of the middle 

 in extension and of the ends in initiating the righting movements. 



3. Shrinking movements, involving the longitudinal muscles only. 

 These may be confined to the more irritable ends, or they may be 

 general, involving the whole body. They have one obvious character- 

 istic distinguishing them from the use of the muscles in locomotion. 

 In the latter the muscular contractions pass along the body progres- 

 sively from segment to segment. In shrinking, however, the body. 

 or at least the active portion of it, acts as a whole and suddenly. 



A second characteristic distinguishes them from the similar move 

 ments of many forms such as the leech, Clepsine. They occur singly 

 only in their weakest form. With increasing stimulation there is a 

 tendency to the production of a quick succession of movements. 

 Clepsine rolls into a ball and remains quiescent in a high state of 

 muscular tension; but such states are unstable in the earthworm 

 and lead to a rapid succession of contractions. Perichseta exhibits 

 these sudden shrinking movements in a very high degree and they 

 have given it the common name of eel-worm. Its form and habits are 

 obviously not adapted to such a protective device as rolling into a 

 ball and remaining quiet. After a single shrinking movement of 

 the weak type or even after a strong series of movements it may 

 remain motionless in a slightly contracted state, which appears 

 rather as an exhibition of sluggishness than of muscular tension, 

 although it suggests the state of "deceptive quiet," which Whitman 

 describes in the leech. 



