FORM-REGULATION IN CERIANTHUS. 117 



dition in this case is evident. Opening of the piece must of 

 course lead to extensive contraction, and fixation of these forms 

 likewise causes extreme distortion as regards details, even after 

 anesthesia. In external examination of the piece it could be 

 seen, however, that a wide space between mesenteries existed 

 here in the new tissue and from this region the large tentacle 

 arose. What the course of the circulatory currents may have 

 been it is also impossible to say. The parts which fused about 

 this region were a part of the aboral end and a part of the longi- 

 tudinal cut surface of the oesophagus, a part of the aboral end, 

 the longitudinal cut surface and a part of the oral end of the 

 body-wall. It is not impossible that both orally directed cur- 

 rents along the body-wall and aborally directed currents along 

 the oesophagus may have been concerned. Moreover, regulative 

 changes may have occurred in the distribution and direction of 

 movement of the cilia. Thus, except for the great space between 

 mesenteries, there is no definite evidence regarding the special 

 factors concerned in the origin of this peculiar tentacle. Never- 

 theless, I think the conclusion is justifiable that the conditions of 

 origin are not different in this case from those in cases already 

 discussed. It is certain at any rate that some degree of disten- 

 sion is necessary for the formation of these aboral tentacles. 



One important difference between the aboral tentacles and oral 

 tentacles appears in both pieces, viz., the difference in time of 

 appearance. In both cases the marginal tentacles at the oral 

 end appeared within a few days after section, and the labial ten- 

 tacles somewhat later, but the tentacles on the aboral end appeared 

 only after about two months when the internal pressure was de- 

 creasing and the pieces were becoming reduced in size. This 

 difference in the time of appearance directs attention to an impor- 

 tant problem, viz., that of polarity so-called. Is the later ap- 

 pearance of the tentacles at the aboral end to be accounted for 

 by a difference in physiological condition between the two ends 

 such that under stimuli the oral end gives rise to tentacles in a 

 much shorter time than the aboral end or is it possible that in 

 consequence of the chance relations between mesenteries oesopha- 

 gus and body-wall in the two cases cited the stimulus became 

 effective only at a much later stage than at the oral end ? 



