April 14, 1916] 



SCIENCE 



519 



more or less dedifferentiation and rejuve- 

 nescence and then by reproduction of a new 

 individual. In agamic reproduction in gen- 

 eral such physiological isolation is a funda- 

 mental factor. Physiological isolation may 

 occur in consequence of continued growth 

 in size or length of the body to such an ex- 

 tent that some part becomes physiologically 

 isolated. Second, it may also occur in con- 

 sequence of decrease in metabolic rate in 

 the dominant region, thus decreasing the 

 range of dominance, until finally the limit 

 of dominance is less than the length of body 

 along the axis concerned. Third, physio- 

 logical isolation may also result from a de- 

 crease in conductivity in the path of trans- 

 mission, thus decreasing the range of effec- 

 tiveness of the transmitted excitation, or in 

 extreme cases blocking it. And finally, 

 physiological isolation may result from the 

 local action of an exciting factor on a sub- 

 ordinate part, increasing its metabolic rate 

 to such an extent that it becomes independ- 

 ent of, or insusceptible to the dynamic 

 changes transmitted from the dominant 

 region. The best proof of the correctness 

 and adequacy of this conception lies in the 

 fact that experimental determination and 

 control of physiological isolation and repro- 

 duction are possible, either in plants or 

 animals, in all these ways. To mention only 

 one ease, in many plants and in various 

 simple animals we can induce agamic repro- 

 duction, not only by inducing growth in 

 size, but by inhibiting or removing the 

 apical dominant region. 



In order that the physiologically isolated 

 part may give rise to a new individual it 

 must either retain to some degree in its 

 protoplasm the axial gradient or gradients 

 determined in it while it was still physio- 

 logically a part of the parent individual, or 

 else new gradients must be determined in 

 it by the differential action of external 

 factors. We find both these possibilities 



realized in nature and in experiment. In 

 short, the phenomena of agamic reproduc- 

 tion in both plants and animals afford very 

 strong evidence in support of this concep- 

 tion of the organic individual. 



Gametic reproduction differs from agamic, 

 first, in that the gametes are more highly 

 differentiated, physiologically older cells 

 than those concerned in agamic reproduc- 

 tion and require in most cases the special 

 conditions of fertilization to initiate the 

 process of reproduction and rejuvenes- 

 cence ; second, in that the isolation of these 

 cells from the parent body in multicellular 

 forms is not directly connected with the 

 range of dominance in the individual, but 

 seems to be rather a process of elimination 

 or extrusion of cells which, so far as the 

 parent body is concerned, have completed 

 their life-cycle, are approaching death and 

 have no further role to play as physiolog- 

 ical parts of the body and are got rid of 

 like other inactive waste material. 



One or two other points require brief con- 

 sideration. I have endeavored to make it 

 clear that the physiological integration of 

 protoplasmic parts or of cells into an indi- 

 vidual with a definite characteristic orderly 

 behavior in space and time is not self-deter- 

 mined by some sort of organization inherent 

 in the protoplasm, nor by some non-mech- 

 anistic integrating principle such as 

 Driesch 's entelechy, but in the final analysis 

 by the relation of the protoplasm or cells 

 concerned to the environment, primarily 

 the external environment, though in the 

 individuation of parts of an organism the 

 intra-individual environment may be the 

 effective factor. In fact, physiological indi- 

 viduality is fundamentally the result of 

 interrelation between living protoplasm and 

 its environment. The fact that morpholog- 

 ical and physiological order in development 

 and evolution are primarily superficial, as 

 for example in the protozoa and in most 



