FORM-REGULATIONS IN CERIANTHUS. 283 



moved very little during the first three to four weeks after sec- 

 tion, i. c., before regeneration of the oral structures was well ad- 

 vanced. In short, the collapsed specimen and the specimen - 

 collapsed or not - - in which the oral structures are not well de- 

 veloped, do not exhibit the typical behavior of the species as 

 regards movement. Probably in the one case the absence of 

 distension brings about some change in the internal stimuli which 

 inhibits the motor impulses to a greater or less extent. In the 

 other case the most highly organized portion of the body - - the 

 oral region - - is absent and the reactions of the pieces are much 

 less vigorous and effective. 



To sum up : two possible factors in the elongation of pieces 

 have been suggested ; the one, tension upon the terminal regions 

 of the body in consequence of the impact of enteric circulatory 

 currents against the wall ; the other, tension upon the tissues in 

 the longitudinal direction in consequence of movement over sur- 

 faces accompanied by some degree of adhesion. 



It is impossible to determine at present whether one or the 

 other of these factors is chiefly concerned, or whether both play 

 important parts in the change of form. It may be that other 

 unknown factors are concerned, but it is highly improbable that 

 there is any mysterious internal ultra-physico-chemical factor 

 which brings about a characteristic form. Mention has already 

 been made of the fact that collapsed pieces never undergo this 

 change of form, but depart farther and farther from the " typical ' 

 form. Now it is possible to keep a specimen collapsed by means 

 of a very small opening at one end or elsewhere, provided this be 

 reopened frequently. It is difficult to understand how such an 

 opening should interfere with any internal or " vitalistic " factor 

 capable of causing return to the typical form. Here again ex- 

 periment indicates the impossibility of explaining the facts with 

 the aid of Driesch's hypothesis (Driesch, '01, '03). 



Both of the hypotheses suggested belong in one category, viz., 

 that of mechanical tension. Whether this tension brings about 

 simply mechanical deformation of the tissue elements, or whether 

 it acts as a functional stimulus to which the tissues react by 

 growth, cannot readily be determined. Probably both mechan- 

 ical deformation and growth occur ; indeed, it is probable that 

 the former brings about the latter. 



