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Upon this point. Professor Allman observes, that to suppose 
that “ all protoplasm is identical where no difference cognis- 
able by any means at our disposal can be detected, would be 
an error. Of two particles of protoplasm, between which we 
may defy all the powers of the microscope, all the resources 
of the laboratory, to detect a difference, one can develop only 
to a jelly-fish, the other only to a man; and one conclusion 
alone is here possible — that deep within them there must be a 
fundamental difference which thus determines their inevitable 
destiny, but of which we know nothing, and can assert nothing 
beyond the statement that it must depend on their hidden 
molecular constitution. In the molecular condition of proto- 
plasm there is probably as much complexity as in the disposi- 
tion of organs in the most highly differentiated organisms ; 
and between two masses of protoplasm indistinguishable from 
one another there may be as much molecular difference as 
there is between the form and arrangement of organs in the 
most widely separated animals or plants.” 
There is, doubtless, much that is attractive in this theory, 
that the “ molecular constitution ” of protoplasm differs in 
different organisms, and that to variations in this respect are 
due the striking differences in the vital phenomena which 
they exhibit. Not only is this theory a fascinating one, but 
it would even find some sort of support in the well known 
phenomenon of “ allotropism ” amongst inorganic substances. 
It must be borne in mind, however, that it is only a theory, 
and that nothing like positive proof can be brought forward 
in its favour. If such differences in molecular constitution 
really exist in the protoplasm of animals and plants, they must 
be as endless as are the variations in the degree and kind of 
the vital phenomena which these exhibit, while, in any case, 
they are purely hypothetical. It should also be borne in mind 
that this theory is only a revival, in a subtler form, of the 
hypothesis that life is the result of organisation ; for it cannot 
be denied that “ molecular constitution ” is only a kind of 
organisation ” upon such a lilliputian scale that it cannot 
be demonstrated even by the microscope, and can only be 
grasped by the “ scientific imagination.” 
In the above connection there is one point which deserves 
a passing notice. It has, namely, been commonly assumed 
that as the life of a Moner or a unicellular organism is seated 
in a single, often microscopic spherule of protoplasm, so a 
complex, multicellular organism, may be properly regarded as 
a mere collection of such units, and its life as a mere agglo- 
meration of the functions and activities of these. It is true, 
no doubt, that in one of the higher animals or plants, each 
