REGENERATION AND LIABILITY TO INJURY 103 



thrown off. King has found that in asterias, regeneration takes place 

 more rapidly from the base than at a more distal level. It may 

 appear, at first thought, that the more rapid regeneration of the arm 

 at the place at which it is usually thrown off may be associated with 

 its more frequent loss at this region in other words, that the more 

 rapid regeneration has been acquired by the region at which the arm 

 is generally broken off. This interpretation is, however, excluded by 

 the fact that, in general, the nearer to the base the arm is cut off, so 

 much the more rapid is its regeneration. In other words, the more 

 rapid regeneration of the arm at the base is only a part of a general 

 law that holds throughout the arm. If the proposition is reversed, 

 and it is claimed that the arm has acquired the property of breaking 

 off at the base, because it regenerates more rapidly at that level, the 

 following fact recorded by King is of importance, viz. that, although 

 the arm regenerates faster at the base, yet a new arm is not any 

 sooner produced in this way, since there is more to be produced and 

 the new arm from the base may never catch up to one growing less 

 rapidly from a more distal cut-surface, but having a nearer goal to 

 reach. 



The results of our examination show that those forms that are 

 liable to have certain parts of their bodies injured are able to regener- 

 ate not only these parts, but at the same time other parts of the body 

 that are not subject to injury. The most remarkable instance of this 

 sort is found in those animals having breaking-joints. In these 

 forms, we find that regeneration takes place both proximal and distal 

 to this region. If the power of regeneration is connected with the 

 liability of a part to injury, this fact is inexplicable. 



Turning now to the question as to whether regeneration takes 

 place in those species that are subject to injury more frequently or 

 better than in other species, we find that the data are not very com- 

 plete or satisfactory for such an examination. It is not easy to ascer- 

 tain to what extent different animals are exposed to injury. If we 

 pass in review the main groups of the animal kingdom, we can at 

 least glean some interesting facts in this connection. 



In the protozoa nucleated pieces have been found to regenerate 

 in all forms that have been examined, including amoeba, difflugia, 

 thalassicolla, paramcecium, stentor, and a number of other ciliate 

 infusoria. 



In the sponges it has been found by Oscar Schmidt that pieces 

 may produce new individuals, but how widely this occurs in the group 

 is not known. In the ccelenterates many forms are known to regen- 

 erate, and it is not improbable that in one way or another the process 

 occurs throughout the group. The hydroid forms, hydra, tubularia, 

 parypha, eudendrium, antennularia, hydractinia, podocoryne, etc., 



