2O2 C. M. CHILD. 



of the margins and the possible cause for this delay has been 

 indicated above. 



If the length of the tentacles is dependent upon internal pres- 

 sure, either general or local, there is no reason why the tentacles 

 on the lowest part of the margin should not finally attain the 

 same length as those on the highest part. They will attain this 

 length later than the others because the first stages in their 

 regeneration are delayed. Other factors such as the difference 

 due to difference in level (see Child, '03^) may prevent the com- 

 plete equalization in length, but there is always a close approxi- 

 mation to equality. Evidently then this regulative process does 

 not differ essentially from others which have been discussed. 

 The same principles which were applied to those are applicable 

 here. In fine, the equalization in length of the tentacles is 

 exactly what might be expected if internal pressure is the chief 

 factor in determining their length. 



The equalization of the tentacles presupposes nearly equal 

 growth in the tentacular region on all parts of the circumference 

 but the reduction in obliquity of the disc is apparently a compen- 

 satory process. Either the body-wall beneath the lower portion 

 of the disc must undergo increase in length, or the body-wall 

 beneath the highest portion must undergo decrease in length, or 

 finally, both these changes must occur in order that the disc 

 may attain a position at right angles to the longitudinal axis. 

 No consideration of the conditions of internal pressure will, in 

 my opinion, afford any means of explaining this compensatory 

 regulative change. On the other hand I think there is little 

 doubt that it is the result of certain characteristic activities of the 

 animal, viz., its orientation in space. Loeb ('91) called attention 

 to the remarkable power of orientation in Cerianthus and showed 

 that in whatever position it was placed the effort was made to 

 bring the longitudinal axis or at least its oral portion into a 

 vertical position, and that having once attained this position 

 the animal remains quiet until other stimuli bring about move- 

 ment. My own observations agree fully with Loeb's as regards 

 this point. The ability of pieces lying on the flat bottom of 

 aquaria to bend the body at right angles and so lift the oral 

 portion into a vertical position is most striking and has formed a 



