/2 C. M. CHILD. 



distance to which the membrane spreads between the surfaces 

 depends upon its composition and the degree of divergence 

 of the surfaces, just as in the case of the fluid film. The 

 thicker membrane with greater resistance will grow farther just 

 as the film with less surface-tension will spread farther, other 

 things being equal. Even the elasticity of the newly formed 

 membrane is paralleled by the tension to which the fluid film is 

 subjected. In both cases the margins of the space may be 

 approximated by this tension and thus permit further spreading of 

 the connecting film or membrane. 



The illustration of the fluid film has been employed primarily 

 as an analogy. It is not to be supposed that the thin membrane 

 growing between two cut surfaces behaves in all respects like a 

 fluid film extending across an angle. Yet the close parallelism 

 between the two series of phenomena must raise the question as 

 to whether after all the growth of new tissue from a cut surface in 

 Cerianthus may not be, at least to a large extent if not entirely, 

 determined by the laws which govern the behavior of fluids. The 

 following facts point toward this conclusion : except so far as heal- 

 ing of a cut surface is concerned new tissue arises from a cut sur- 

 face only when it is in contact with another, the thin membrane 

 of new tissue which is under tension spreads between diverging 

 cut surfaces to a certain point, beyond which no growth occurs, 

 unless the surfaces are brought nearer together ; the point where 

 growth ceases differs in different species, depending on the quality 

 of the membrane ; the cut surfaces may themselves be approxi- 

 mated by the tension of the membrane and so further growth of 

 the membrane made possible ; the free margin of the membrane 

 is always concave in the direction of growth, /. c., the margins of 

 the membrane extend further than its middle region. In all of 

 these respects the thin membrane and the fluid film behave simi- 

 larly. The conclusion is at least probable that the similarity in 

 behavior is due to the fact that similar conditions are present. I 

 think it probable, therefore, that the appearance and growth of 

 new tissue from the cut surfaces of the body of CcriantJnts is 

 governed, at least to a large extent, by the laws of capillarity. 

 Qf course the cellular structure of the tissue may complicate con- 

 ditions, and the thickening and structural differentiation which 



