I IO C. M. CHILD. 



As regards the relation between rapidity and amount of growth 

 and the level at which these supplementary discs are situated, my 

 own observations agree with those of Loeb. He found that the 

 rapidity and amount of growth decreased with increasing distance 

 from the oral end and that the extreme aboral region was incapa- 

 ble of producing supplementary discs. These results also agree 

 with the observations described in my second paper (Child, '03/7) 

 concerning the effect of position upon rapidity and amount of 



regeneration. 



General Considerations. 



The formation of supplementary discs constitutes another 

 chapter of evidence on the role of internal water-pressure in regu- 

 lative processes in Cerianthus. It is scarcely necessary, I think, 

 to devote further space to the consideration of Loeb's view that 

 tentacle-reduction is due to loss of intracellular turgor. It cer- 

 tainly does not account for the observed facts to which Loeb 

 attempts to apply it. A knowledge of the structure of the animal 

 would have made such conclusions impossible. 



These experiments show most clearly that continuous or nearly 

 continuous tension due to internal pressure is absolutely essential 

 for the persistence of form and structure in Cerianthus. In its 

 absence atrophy always occurs. 



Doubtless various changes in the intracellular turgor occur 

 during reduction and atrophy but these must be regarded a 

 result rather than a cause, for so long as the tissue is subjected 

 to the tension caused by internal water-pressure these changes 

 in turgor do not occur. 



The fact that the changes in Cerianthus which Loeb regarded 

 as change in turgor are not such does not of course detract in 

 any way from the value of the osmotic hypothesis in general. 

 It is important, however, that the effects of distension of internal 

 cavities with water or other fluids should be distinguished from 

 the effects of intracellular phenomena. The case in hand is simply 

 an incorrect application of the osmotic hypothesis. 



On page 57 Loeb ('91) makes the following statement regard- 

 ing the supplementary disc formed in the middle region of the 

 body : " Diese neugebildete Kopf, b. Fig. 2, scheint ganz auf 

 dem Ektoderm zu sitzen." It would not have required an ex- 



