Studies of Tissue Growth 461 



is greater in the individuals growing five arms than in those grow- 

 ing fewer. The above reasoning depends largely upon the rate 

 of regeneration itself as a factor acting upon the old body tissue 

 to inhibit its growth or to cause it to decrease in size. I do not 

 believe that this is entirely important and offer the above suggestion 

 only as a possibility. The facts furnished by the medusa, Cas- 

 siopea, indicate that the decrease in body size is in a greater pro- 

 portion than the increase in growth rates of new arms in speci- 

 mens extensively injured as compared with those less injured. 



We have now considered the relation between the degree of in- 

 jury and the rate of regeneration in three different species of ani- 

 mals. The three species clearly show that the extent of injury 

 fails to exert an influence in any one definite direction over the 

 rate of regeneration in all animals. Former experiments which have 

 seemed to indicate that the rate of regeneration is increased in 

 animals injured to greater degrees have either been performed 

 on crustaceans where growth is not continuous and where the 

 influence of regeneration on the molting cycle introduces a com- 

 plication, as Emmel's work so clearly demonstrates, or else have 

 been conducted with too small a series of animals to justify general 

 conclusions. Scott's study ('07) of the rate of fin regeneration in 

 more than 100 individuals of Fundulus heteroclitus shows by 

 careful calculations that the degree of injury exerts no influence 

 either to increase or decrease the rate of regeneration in this fish. 

 These experiments on the fish, along with those of Zeleny on Crus- 

 tacea, an ophiuran and a medusa, Emmel's study of larval lob- 

 sters and my experiments on Cassiopea and two Ophiurans would 

 seem to justify the following conclusion. By varying the extent 

 of injury in several animal species there is no definite influence 

 exerted in any one direction on the rate of regenerative growth. 



Morgan ('06, p. 460) draws a resemblance between the differ- 

 ences in rate of regeneration at different levels on an appendage 

 or body and Zeleny's idea regarding the relation between the regen- 

 eration rates of the new parts and the number of parts removed. 

 "If the distal end of the tail is removed it regenerates more slowly 

 than when more of the tail is cut off. Thus the more the material 

 removed the greater the rate of regeneration of the new part. 



