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RAYMOND PEAWL 



sliorteuing or contraction of the opposite side. We may now 

 consider the evidence as to whether or not the turning away 

 is actually due to a lengthening of the side stimulated. 



Very little evidence can be obtained regarding this from 

 observation of the normal moving animal, because the 

 general appearance in the turning would be the same 

 whether it were due to a shortening of one side or a 

 lengthening of the other. The results from certain sorts of 

 operation, however, give definite evidence on the question. 



A specimen split longitudinally in the posterior end, as 

 shown in Fig. 17, a, and the cut was extended forward to the 

 posterior border of the head region. Several days were 



Fig. 17. — «. Operation diagram, h. Showing side A supported on 

 B. For further explanation see text. (Tiie pliarynx is omitted 

 for the salve of clearness.) 



allowed for recovery from the shock of the operation, care 

 being taken to prevent the two parts from growing together 

 again. By this time the cut edges had healed well, and the 

 specimen was in good condition for experimentation. The 

 results of mechanical stimulation were as follows: strong 

 stimulation of the head or anterior part of the body on either 

 side caused the negative reaction; the anterior end turned 

 away from the stimulus. But it was possible to tell in this 

 case which of the two pieces or halves of the body were 

 effective in producing the turning. It could be seen clearly 

 that the half stimulated, immediately on stimulation, flattened 



