682 



EAYMOND PEARL, 



and its reactiuns observed. Evidently, so far as injury of 

 the mechanism by the operation is' concerned, such a piece 

 is in essentially the same condition as the pieces described 

 in the previous experiment. It has only one complete side 

 of the body. The piece when inverted squirmed about consider- 

 ably at first, but gave no indication whatever of the normal 

 spiral reaction. In a short time the violent movements ceased, 

 and a notch Avas noticed in about the middle of the uncut 

 edge (cf. Fig. 40, h). This soon grew larger, and extended 

 more and more towards the ends of the piece, as shown in 



I'lG. 10. — a. Operation diagram. Heavy lines indicate llie ciifs. 6, c, 

 and rl. Successive stages in tlie righting reaction of the piece A of 

 diagram a. e and /. Cross-sections througli A at two successive 

 stages in the righting process. See text for further explanation. 



c and (J. ]iy close observation the cause of this appearance 

 was found to be that the thin mobile edge was folding 

 under and attaching its ventral surface along the Ijottom. A 

 cross-section through the worm at this stage had the outline 

 shown in e. As soon as a considerable portion of the edge 

 had so folded under and become attached, the piece gave 

 a series of strong contractions and literally " Hopped " over 

 the attached edge and came down right side up. A stage in 

 tliis ])rucess is shown in cross-section in /. Tliis behaviour 

 was so peculiai', and at the same time })recise, that the 



