274 



C. M. CHILD. 



either in the structure of the protoplasm or as a governing prin- 

 ciple distinct from physical and chemical factors to which the 

 latter are subordinated. On the other hand, it is possible, at 

 least theoretically, to regard organic form as the resultant of the 

 complex of physical and chemical conditions internal and external 

 which affect the protoplasm. According to this view, organic 

 form is not strictly speaking inherent in the living substance ; 

 but results indirectly from its activities and its environment. 



The experiments to be described demonstrate, I believe, that 

 in the absence of internal water-pressure the living substance of 

 Ccriantliits is absolutely incapable of producing the typical form 

 of this animal. It is not merely that the parts are formed and 

 remain collapsed in the absence of water-pressure ; either they 

 are not formed or their form is atypical. The appearance of the 

 tentacles is delayed or is inhibited ; the growth of the disc and 

 the oesophagus does not occur when the internal pressure is 

 reduced below a certain point. Thus it is possible in this case 

 to demonstrate a general relation between internal water-pressure 

 and growth. 



The question as to whether any relation between localized 

 growth and localized internal pressure exists must not be con- 

 fused with the preceding question as to a general relation be- 

 tween the two phenomena. It is possible for instance to sup- 

 pose that the region where new tentacles shall appear is deter- 

 mined in some unknown manner, but that the internal pressure 

 is a factor in causing their growth after their position has been 

 determined. On the other hand, it is possible to conceive that 

 the position of these structures is determined by local pressure 

 due to currents in the enteron (the " circulatory currents"). It 

 cannot be claimed for my experiments thus far that they decide 

 which of these two possibilities is correct. Certain of the data, 

 however, appear to me to indicate that the local pressure due to 

 currents may play a certain role in determining the position of 

 the marginal tentacles. Concerning the labial tentacles there is as 

 yet no definite evidence and this fact must constitute a weak point 

 in the evidence, at least until further experiments can be performed. 



Time need be taken here only for a brief consideration of the 

 possibility of a direct relation between local internal pressure and 



