282 C. M. CHILD. 



comes distended with water after closure it may be impossible or 

 difficult for the water to gain entrance into the intermesenterial 

 chambers of the folded part and so this may fail to be distended ; 

 if it is not distended it will be compressed to a greater or less 

 extent by the adjacent distended regions. In this manner it is 

 possible to produce experimentally cases in which only a part of 

 the circumference becomes distended with water after closure. 

 In all such cases it is found that the tentacles appear only on the 

 distended portions. If the infolded or compressed portions be- 

 come distended later, tentacles appear. 



Provided the aboral end is kept open long enough, tentacles 

 may appear in those regions where the mesenterial chambers are 

 sufficiently open to permit the entrance and circulation of water. 

 Of course the formation of tentacles is much slower in this case 

 than when the piece is permitted to distend, and they never at- 

 tain very great length. Since the regeneration of the tentacles is 

 very slow and does not proceed far, this method is less satisfac- 

 tory than the first. 



By both of these methods it is possible to bring about local 

 inhibition of tentacle-regeneration. In some cases the folded or 

 compressed region includes only one or two mesenterial cham- 

 bers, and here only one or two tentacles are inhibited or delayed. 

 In pieces with slightly irregular oral margins where closure is 

 irregular there is often great irregularity in the tentacles, some 

 appearing early, others late, but in every case it can be deter- 

 mined that the tentacles appear first on those parts where dis- 

 tension and the circulation of water is least hindered, and rice 

 versa. 



There is very rarely any difficulty in distinguishing the dis- 

 tended portions of the body from those that are collapsed or 

 compressed ; the former appear somewhat translucent and the 

 surface is smooth ; the latter are opaque and usually more or 

 less wrinkled. Moreover there is a distinct difference in color 

 between distended and collapsed portions, the former being al- 

 ways lighter in color, since distension stretches the body-wall 

 and the stripes (in C. solitarius] are farther apart or the pigment 

 granules (in C. membranaceus} less densely distributed. Thus 

 distended parts can usually be distinguished at a glance from 



