Studies of Tissue Growth 441 



Small equilateral triangles cut so that a portion of the disk pe- 

 riphery forms one side of the triangle (Fig. 6A) will pulsate and 

 finally form cup-shaped bodies. The cup-shape is here again the 

 nearest possible approach to the circular medusa form. New 

 tissue regenerates from the two cut edges, ac ac, of the triangle 

 and a tendency of the piece to fold or roll up brings together the 

 apices a-a formed by the disk periphery and the cut sides. These 

 two apices of the triangle unite and the third apex c folds over so 

 as to form the base of the cup. The wall of the cup is completed 

 by the fusion of new tissue from the two cut sides ac ac of the tri- 

 angle (Fig. 6B). In this case again the new tissue ceases to grow 

 after the cup-shape becomes established. 



These experiments with the three differently shaped pieces of 

 medusa-disk were repeated a second time, and in all ten pieces 

 of each shape were employed, but no deviation from the above 

 descriptions was observed. The conclusion is evident that these 

 disk pieces possess a high degree of regulatory ability and in all 

 cases tend to assume as near as possible a circular shape approach- 

 ing the original disk form. The fact is of importance that this 

 regulatory tendency seems to possess the power of controlling or 

 inhibiting regenerative activity. Regenerating tissue ceases to 

 grow when the circular form is attained. 



The writer does not pretend to explain this peculiar fact, though 

 it is probably comparable to the adjustment existing in normal 

 organisms, which prevents certain tissues from growing to an 

 extent that would cause them to become displaced. An excessive 

 proliferation of tissue from any organ would destroy the usual 

 body symmetry but the interaction of some unknown complex of 

 factors maintains a morphological equilibrium and prevents such 

 occurrences. At times this equilibrium is disturbed and hyper- 

 trophy or excessive tissues result. It is important to note that 

 these small pieces of medusa disk possess this power of perfect 

 coordination. 



