FORM-REGULATION IN CERIANTHUS. 2O3 



constant feature of my experiments. In pieces with oblique 

 discs an interesting modification of this orienting reaction has 

 been observed. The oral portion of the body was brought into 

 a vertical position and furthermore the effort was made by means 

 of unequal contraction of the muscles on the two sides of the 

 body to bring the disc into a horizontal position at right angles 

 to 'the longitudinal axis. During the earliest stages of regener- 

 ation the pieces never react normally but after they become 

 closed and distended the reactions gradually appear. In the 

 oblique pieces this reaction is already very distinct at the stage of 

 Fig. 5. When the pieces are left undisturbed they orient them- 

 selves so that the disc appears nearly horizontal and the body 

 below it nearly vertical. That the muscles of the two sides 

 must be unequally contracted is evident. A sudden tactile 

 stimulus or other irritation causes a marked change in the rela- 

 tion of parts. The specimens undergo sudden contraction and 

 the obliquity of the disc increases greatly. The stronger the 

 stimulus and consequently the more complete the contraction of 

 the muscles the greater the obliquity of the disc in such cases. 

 Left to themselves, the animals gradually extend, become filled 

 with water again and resume the former position. The increase 

 of the obliquity of the disc in the contracted condition results 

 from the difference in the degree of contraction at different points 

 of the circumference in the distended oriented condition. A 

 brief consideration will be sufficient to render this clear ; in the 

 normal animal a stimulus of this kind causes an equal degree of 

 contraction in all the longitudinal muscles and there is no reason 

 to suppose that the effect is different in the oblique pieces. The 

 increase in the obliquity of the disc which accompanies contrac- 

 tion in oblique pieces must result from a difference in condition 

 of the muscles on the opposite sides of the body. If for instance 

 we suppose that the muscles of the body beneath the highest 

 part of the oblique disc are partially contracted in the effort to 

 bring the disc into a horizontal position it is evident that these 

 muscles will contract less in consequence of the sudden stimulus 

 than those on the opposite side of the body and consequently 

 the angle between disc and longitudinal axis must decrease. 

 During the earlier stages of regulation the animal is unable to 



