PHYSIOLOGY: C M. CHILD 
171 
In the plants and lower animals the physiological isolation of a part 
usually results in reproduction of some sort, the character of the repro- 
duction varying according to the conditions. Certainly the simpler and 
probably all agamic, or, as we commonly call them, asexual reproductive 
processes belong in this category, although additional factors are con- 
cerned in some. Reproduction under these conditions of physiological 
isolation means simply that the isolated part loses more or less com- 
pletely its characteristics as a part, since the correlative conditions which 
determined them are no longer acting, and becomes a new individual, 
either with the persistence of the original metabolic gradients, or with 
the development of new ones through the action of external factors, both 
cases being represented in nature. We see these forms of reproduction 
very commonly in both plants and the lower animals. For example, 
in some of the worms, when the body attains a certain length, the pos- 
terior region becomes a new animal exactly as it does when we isolate it 
physically by cutting it off, and it can be shown that this reconstitution 
results from physiological isolation. ^ In plants a new bud, which is 
a new plant individual, arises at a certain distance from the one previ- 
ously formed, etc. 
These reproductions have been variously controlled and modified in 
plants and I have found it possible to control them in animals. Growth 
is not necessary for their occurrence, for we can decrease the physiologi- 
cal limit of size of the individual, i.e., the length of the gradient, by de- 
creasing the metabolic rate of the whole or of the apical region alone. 
One of the simplest ways of inducing such reproduction is to cut off the 
dominant region or decrease or inhibit its metabolic activity. This 
results in lowering the rate in all other parts and so in shortening the 
gradient, and this in turn results in physiological isolation of the more 
remote parts. Sometimes, when the gradient is nearly or quite elimi- 
nated, the individual breaks up into many new individuals, perhaps into 
single cells, each of which later repeats the process of development. 
Many cases of spore formation in the plants and lower animals are of 
this nature. 
This conception of the organic individual throws light on many ques- 
tions heretofore obscure. It not only accounts for the orderly behavior 
in space and time of the organism during development and for the agamic 
reproductions, but it enables us to understand how a multitude of axes 
or polarities, extending in all possible directions, can exist in different 
cells and organs at the same time with a general axis or axes of the 
whole organism. 
