l88 UNIVERSITY OF MISSOURI BULLETIN 



This latter has been termed "regulation." After it has oc- 

 curred the specimen may grow to the size of the original. 



Another phenomenon, is the polarity which the pieces 

 exhibit, no matter how they may be cut. The axes of the 

 old body somehow become those of the new. It is as though 

 every part of the original were laid down on certain lines and 

 these lines persisted in the piece removed. This is termed 

 the "polarity" of the organism. Heteromorphosis is, of course 

 an exception, though not an irreconcilable one. 



This power of regeneration is widely distributed among 

 animals. In a general way, those forms which have as a 

 part of their normal life cycle marked powers of a sexual 

 multiplication (budding, fission and the like) are found to 

 possess the greatest powers of regeneration, while the more 

 specialized forms, which reproduce only sexually, can no more 

 than heal wounds of limited extent, or replace lost appendages, 

 as does the crayfish. 



The results thus far obtained from studies upon regenera- 

 tion have been in a way disappointing. We have been con- 

 fronted with the same riddles as in the study of ordinary 

 development, and the present day conclusion is that regenera- 

 tion is but an aspect of the phenomenon of growth, and that 

 only when we explain the one shall we comprehend the other. 

 The study has thrown much light upon some special problems 

 like that of differentiation in adult organisms, and, for the 

 future, one of the most interesting possibilities is that the facts 

 brought out may at any time bring results of revolutionary 

 value in dealing with pathological conditions in man and in 

 those animals and plants most immediately connected with 

 his welfare. 



ANIMAL BEHAVIOR 



Let us pass to another illustration of experimental work. 

 The study of animal behavior, while overlapping the field of 

 the psychologist, has become a part of experimental zoolog>r 



