July, 1923 ] 
ALLEN — POTENTIALITIES OF A CELL 
391 
related with this loss, whether simultaneous or subsequent, was the dis¬ 
appearance of chromatophores. In other ways the range of potentialities 
has been limited, so that the cell can assume (so far as known, with the 
possible exception of one species) only the flagellate form. The plasticity 
of the pigmented species, as shown by the number of phases possible to 
the organism, has been reduced. 
Some of the changes accompanying the complete loss of potentialities 
consist in the modification, rather than the loss, of certain powers of re¬ 
sponse. The specialization in adaptation to a parasitic mode of existence 
implies that the race remains under a greater variety of conditions in a 
phase suited only to parasitic nutrition. That there has been a real change 
in responsive power is shown by the great difficulty of keeping these or¬ 
ganisms alive in any habitat other than that to which they are so narrowly- 
adapted. 
On the other hand, new potentialities have appeared. Without much 
doubt the adaptation to a parasitic existence has involved the acquisition 
of new powers of digesting and assimilating the types of nutrients now 
available. New potentialities certainly show themselves in the develop¬ 
ment of intracellular structures, notably the elaborate neuromotor appara¬ 
tus recently described in detail by Kofoid and his students. It is quite 
possible, too, that the loss of the power of passing into certain phases is 
in a measure compensated for by an increased power of responding by rela¬ 
tively small modifications to the minor environmental changes which are 
all that an internal parasite ordinarily encounters during its active life. 
Comparable changes have occurred in the evolution of other protists 
from flagellate ancestors. , Each phase in the history of a slime mold such 
as Stemonitis, except that of the sporange—walled spore, swarm-spore, 
amoeba, microcyst, plasmodium, sclerotium—is duplicated, or simulated, 
in the life cycles of numerous flagellates. So many phases persist that, 
until the course of descent of the myxomycetes is known, it will be impos¬ 
sible to say what, if any, potentialities have been lost. On the other 
hand, new potentialities, leading to the formation of a rather complex 
sporange and capillitium, have been acquired. It is possible, however, 
that some of the potentialities concerned in sporange-formation are not 
really new to the myxomycetes, but are old ones which have been modified 
in time of appearance, in degree, or in duration. In large mea.sure, too, 
there have been modifications in responsive power which affect the dura¬ 
tion of the various phases. 
The life cycle of Stemonitis consists of a series of phases, still with marked 
possibilities of substitution, suppression, and extension, but none the less 
following one another in fairly definite order and in the main incapable 
of inversion. The tendency operating in the pigmented flagellates toward 
some sort of sequence of stages seems to have become more effective. Thus 
the change in fundamental organization which has diminished the flagellate 
