stage, cutaneous
eruption, itching, tingling, sore throat, swelled fauces, salivation,
cough, hoarseness, dyspnoea, etc.; and in the third stage,
oedematous inflammations, pneumonia, pleurisy, diarrhoea,
inflammation of the brain, ophthalmia, erysipelas, etc.; each of which
enumerated symptoms is itself more or less complex. Medicines, special
foods, better air, might in like manner be instanced as producing
multiplied results.

Now it needs only to consider that the many changes thus wrought by one
force upon an adult organism, will be in part paralleled in an embryo
organism, to understand how here also, the evolution of the homogeneous
into the heterogeneous may be due to the production of many effects by
one cause. The external heat and other agencies which determine the
first complications of the germ, may, by acting upon these, superinduce
further complications; upon these still higher and more numerous ones;
and so on continually: each organ as it is developed serving, by its
actions and reactions upon the rest, to initiate new complexities. The
first pulsations of the foetal heart must simultaneously aid the
unfolding of every part. The growth of each tissue, by taking from the
blood special proportions of elements, must modify the constitution of
the blood; and so must modify the nutrition of all the other tissues.
The heart's action, implying as it does a certain waste, necessitates an
addition to the blood of effete matters, which must influence the rest
of the system, and perhaps, as some think, cause the formation of
excretory organs. The nervous connections established among the viscera
must further multiply their mutual influences: and so continually.

Still stronger becomes the probability of this view when we call to mind
the fact, that the same germ may be evolved into different forms
according to circumstances. Thus, during its earlier stages, every
embryo is sexless--becomes either male or female as the balance of
forces acting upon it determines. Again, it is a well-established fact
that the larva of a working-bee will develop into a queen-bee, if,
before it is too late, its food be changed to that on which the larvae of
queen-bees are fed. Even more remarkable is the case of certain entozoa.
The ovum of a tape-worm, getting into its natural habitat, the
intestine, unfolds into the well-known form of its parent; but if
carried, as it frequently is, into other parts of the system, it becomes
a sac-