FORM-REGULATIONS IN CERIANTHUS. 28 I 



total pressure of considerable amount upon the oral end. On 

 the other hand a current passing aborally along the inner mar- 

 gins of the mesenteries or a part of them must finally strike the 

 aboral end -and produce pressure there. Now the effect of these 

 currents may conceivably show itself partly in local growth in 

 region of impact, /. e., where the tension upon the tissues result- 

 ing from the impact of the current is greatest and partly in a 

 diffuse growth or a change of form in accordance with the tension 

 in the surrounding regions to which some degree of the tension 

 is transmitted. Since these currents strike the terminal regions 

 of the body local growth at the ends and elongation of the whole 

 must be the result if they are effective in the manner suggested. 

 In pieces kept without food the elongation must be accompanied 



o o 



14 15 16 17 



by a reduction in the transverse diameter. These suggestions 

 as to the effects of circulatory currents, like those made in previ- 

 ous papers (Child, '04$, ct scq.'] must be regarded at present as 

 merely tentative. They may be entirely incorrect but I think 

 the hypothesis of the effectiveness of circulatory currents as 

 localizing formative stimuli cannot be rejected off-hand. It serves 

 so well as a basis for explanation of various phenomena that it 

 must at least receive consideration. I hope at some future time 

 to obtain experimental evidence regarding this hypothesis. 



The second possibility, viz., that the change of form may be 

 an incidental result of the movements of the animal must also be 

 considered. As noted above, the behavior of typically distended 

 specimens is very different from that of the same pieces during 

 collapse. The creeping habit of Cerianthus is well known ; the 

 animals are able to move about freely, lying upon the side and 

 moving with either oral or aboral end in advance. They move 

 not only on horizontal surfaces, but are able to climb the vertical 

 sides of a glass jar or aquarium. In my aquaria specimens often 



