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104 University of California Publications in Zoology [ V <> L - 18 



INTRODUCTION 



The normal creeping movements of the earthworm proceed as fol- 

 lows. The first movement is a contraction of the circular muscles of 

 the first few segments. This causes an extension of the anterior end. 

 The chaetae now become directed backwards and take hold on the 

 substrate while the longitudinal muscles begin a contraction which 

 draws the next few segments forward. The circular muscles in each 

 segment contract, one segment after another beginning at the anterior 

 end and proceeding posteriorly. Immediately following the circular 

 muscle action the longitudinal muscles contract so that a wave of 

 extension followed by a shortening can be seen to traverse the whole 

 animal. After the first wave of muscular activity is well started 

 posteriorly another may be initiated and at any one time several of 

 these contraction waves may be seen in a normally creeping worm. 



Some years ago Friedlander (1894) showed that in the normal 

 creeping of an earthworm the nervous system played only a small part. 

 When a section of the nerve cord containing ten to twelve ganglia was 

 removed, the movements of the parts of the worm were still perfectly 

 coordinated. The most important part of the activity was the ' ' pull ' ' 

 which the contraction of each segment as the wave progresses gave to 

 the succeeding segments. The wave-like motion of the contractions 

 proceeding down the length of the animal was due, first, to the pull 

 of segments on each other, and, secondly, to the sequence of reflex 

 actions of the nerves in each segment, which are such that the longi- 

 tudinal muscles follow the contractions of the circular muscles. This 

 nervous mechanism is, according to Friedlander, concerned with each 

 segment alone, and there is no passage of impulses up or down the 

 cord. No attempt was made by him to analyze the matter of tension 

 or pull, or to determine whether coordination w r ould proceed without 

 this factor. 



In order to show that the nervous system was entirely secondary, 

 Friedlander cut a worm into two pieces and then joined these two with 

 a thread The creeping movements of the anterior piece gave the 

 necessary pull on the posterior piece through the thread, and the two 

 parts crept along in perfect coordination. In certain special cases, 

 when the nerve cord was destroyed for a short distance without tran- 

 section of the body, the parts anterior and posterior to the cordless 

 region moved together with perfect coordination. According to this 



