200 THE SCIENCE OF BIOLOGY 



matter how the piece 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. Heteromorphosis is, of 

 course, an exception, though not impossible of explanation in 

 terms of the normal polarity. 



The power of regeneration is widely distributed among the 

 lower organisms. Generally speaking, those animals and 

 plants which exhibit in their normal life-cycles marked 

 powers of vegetative reproduction (budding, fission, and the 

 like) are found to possess the greatest capacity for regenera- 

 tion. Specialized forms, which reproduce only by means of 

 germ-cells, can do little more than heal wounds of limited 

 extent or replace lost appendages, as does the crayfish. 

 Studies upon regeneration have shown the nature and extent 

 of regeneration in a wide variety of forms. With these facts 

 known, it has been possible to consider the more subtle 

 factors involved. The problems of regulation and polarity 

 have been attacked in recent years with some degree of 

 success. Study of the conditions under which a piece of 

 an organism forms a complete individual has thrown light 

 upon the nature of the organized system that we call an indi- 

 vidual. 12 Regeneration, regulation, and polarity are part of 

 the larger phenomenon of growth and differentiation ex- 

 hibited by all many-celled organisms. Results in these 

 fields interlock with those obtained in the study of embryonic 

 development. The piece of an organism which regenerates 

 the whole is obviously possessed of the same kind of poten- 

 tiality that exists in embryonic tissue. How adult tissues can 

 thus exhibit embryonic capacities is an interesting problem, 

 the investigation of which may eventually throw light not 

 only upon embryonic development but also upon certain 

 pathological conditions which exist at times in the human 

 body and in the bodies of higher animals and plants. 



Natural Death : The early stages of development, which 



12 Child, C. M., "Individuality in Organisms, 1915." 



