Studies in Tissue Growth 467 



3 The rate of regeneration from a peripheral cut on the Cas- 

 siopea disk is faster the nearer the disk center the cut is made. 

 In the brittle-stars Ophiocoma nisei and Ophiocoma echinata 

 new arms regenerate faster as the old arms are cut off nearer 

 their base of attachment to the body-disk. The nearer the distal 

 end a portion of arm is amputated the slower will a new part 

 regenerate. 



These experiments and those of several other workers all show 

 that the rate of regeneration in diverse species of animals varies 

 with the level of the cut, being faster as the cut surface is nearer 

 the body center. 



4 The rate of regeneration does not bear the same definite 

 relation to the extent of injury in all animal species. 



The medusa, Cassiopea, regenerates each oral arm at a rate 

 which is independent of the degree of injury when replacing either 

 one, two, four or six of its arms. If, however, eight arms are 

 amputated each arm is regenerated at a rate which, after taking 

 account of the probable error, is significantly greater than the 

 regeneration rates in medusae injured to any less extent. 



The brittle-star, Ophiocoma riisei, regenerates either one, two, 

 three, four or all five arms at rates which are not significantly 

 different. In other words, there is no relation between the rate of 

 regeneration of the individual arms and the degree of injury in this 

 species. 



The rate of regeneration for individual arms in Ophiocoma 

 echinata, another species of ophiuran, is fastest when only a single 

 arm is regenerating and successively slower when two, three, four 

 and five arms are being leplaced. The rate of regeneration is 

 slower the greater the extent of injury. 



The facts show that the rate of regeneration does not increase 

 with an increase in the extent of injury in all animals but may 

 actually respond in an opposite manner, or the rate of regeneration 

 may even be independent of the extent of injury. 



5 The unfed disk of Cassiopea decreases in size during regen- 

 eration in direct relation to the number of regenerating arms. 

 Thus while the disks which are regenerating eight new arms grow 

 them at the most rapid rate these disks are also decreasing in size 

 most rapidly. 



