434 Charles R. Stockard 



My ('08) previous study on regeneration in the Scyphomedusa, 

 Cassiopea xamachana, considered the influences of certain in- 

 ternal factors on the rate of regenerative growth. The present 

 account is also concerned with the rate of regeneration in Cas- 

 siopea and in addition includes a study of two species of brittle 

 stars, Ophiocoma riisei and Ophiocoma echinata. 



The level at which the cut is made determines the rate of the 

 ensuing regeneration in the three animals employed. The nearer 

 to the center of the body the tissue is removed the more rapidly 

 will the regenerating tissue grow. An arm regenerates at a faster 

 rate when amputated near its base than when amputated at a 

 more distal point. The growth of the new tissue gradually be- 

 comes slower, however, as the original size is approached. An 

 analogy is found in embryonic growth, the smaller embryo in- 

 creases proportionately much more rapidly in size than does the 

 larger and older embryo. The rate of increase becomes contin- 

 ually slower as the adult size is approached and finally growth 

 ceases at this limit. 



The relation between the extent of injury and the rate of regen- 

 eration will be considered in each of the three species. Finally, 

 the evidence furnished by animals regenerating different amounts 

 of tissue will be reviewed in order to ascertain the nature of the 

 influence exerted by the new growing tissue over the old body 

 substances. 



The experimental part of the investigation was conducted in the 

 Biological Station of the Carnegie Institution at Tortugas, Fla. 

 I w^sh to express my thanks to the Director, Dr. Alfred G. Mayer, 

 for the facilities supplied for this work and for his kindness in 

 preserving the ophiurans after I had gone from the laboratory. 

 The remainder of the work has been done in the Pathological 

 Laboratories of Cornell University Medical College for the Hunt- 

 ington Fund for Cancer Research. 



II MATERIAL AND METHODS 



The medusae are abundant in the somewhat stagnant water of 

 the moat surrounding the old fort at Dry Tortugas Islands. This 



