FORM REGULATION IN CERIANTHUS .-ESTUARII. 5 I 



spherical form (Fig. 24). Such specimens are absolutely inca- 

 pable of burrowing and never regain their usual form, at least no 

 return was observed during a period of something over four months. 

 Frequently, however, the change in shape ceases before the ex- 

 treme condition is reached, e. g., at a stage resembling Fig. 23 and 

 the animal retains this shape afterward. The cessation of the 

 change in shape appears to be a functional reaction of the tissues 

 to the altered conditions to which they are subjected, /. e., the in- 

 creased tension in the body-wall develops increased resisting power, 

 a change similar to that occurring in many other so-called func- 

 tional adaptations. On the other hand, rupture of the body-wall 

 frequently occurs in the enlarged region. These facts demon- 

 strate that the tubicolous habit is an important factor in determin- 

 ing the shape of the body and the functional character of the 

 body-wall. 



VI. Discussion and Summary. 



C. cestuarii demonstrates even more clearly than C. solitarhis 

 the importance of internal water-pressure for regulatory devel- 

 opment and for the continued existence of the body-wall and 

 tentacles. 



On the other hand, there is no evidence that changes in the 

 turgor of the cells themselves play an important or definite role 

 in form-regulation, except that atrophy appears to be accom- 

 panied by a decrease in the turgor of the tissues involved. There 

 is certainly no appreciable change in the turgor of the cell such 

 as Moszkowski ('07, p. 412) describes for Actinia and Actinoloba. 

 If Moszkowski's observations are correct, and certainly observa- 

 tions on CeriantJms do not permit conclusions concerning other 

 forms, they simply afford another illustration of the physiolog- 

 ical differences which may exist in different species. 



The passage of water through the body-wall and the conse- 

 quent distension of the body occurs in Ceriant/ms, as noted above 

 and in my earlier papers (Child, '04b, pp. 276-277), as well as in 

 Actinia and Actinoloba (Moszkowski, '07, p. 412), but it has not 

 been possible thus far to discover any indications of a marked 

 change in turgor of the cells themselves, and the results of my 

 experiments show very clearly that the water in the enteron is an 

 essential factor in form-regulation in CeriantJms. 



