132 ANIMAL PHYSIOLOGY. 
pendent forms of life applies to the higher. All organisms are 
made up of cells or aggregations of cells and their products, 
For the present we may disregard the latter.. When a muscle- 
cell by division gives rise to a new cell, the latter is not identi- 
cally the same in every particular.as the parent cell was origi- 
nally. It is what its parent has become by virtue of those 
experiences it has had as a muscle-cell per se, and as a member 
of a populous biological community, of the complexities of 
which we can scarcely conceive. 
Now, as a body at rest may remain so, or may move in a 
certain direction according as the forces acting upon it exactly 
counterbalance one another, or produce a resultant effect in 
the direction in which the body moves, so in the case of he- 
redity, whether a certain quality in the parent appears in the 
offspring, depends on whether this quality is neutralized, aug- 
mented, or otherwise modified by any corresponding quality in 
the other parent, or by some opposite quality, taken in connec- 
tion with the direct influence of the environment during devel- 
opment. 
This assumption explains among other things why acquired 
peculiarities (the results of accident, habit, etc.) may or may 
not be inherited. 
These are not usually inherited because, as is to be expect- 
ed, those forces of the organism which have been gathering 
head for ages are naturally not easily turned aside. Again, we 
urge, heredity must be more pronounced than variation. 
The ovum and sperm-cell, like all other cells of the body, 
are microcosms representing the whole to a certain extent in 
themselves—that is to say, cell A is what it is by reason of what 
all the other millions of its fellows in the biological republic 
“are; so that it is possible to understand why sexual cells repre- 
sent, embody, and repeat the whole biological story, though it 
is not yet possible to indicate exactly how they more than 
others have this power. This falls under the laws of speciali- 
zation and the physiological division of labor ; but along what 
paths they have reached this we can not determine. 
Strong evidence is furnished for the above views by the his- 
tory of disease. Scar-tissue, for example, continues to repro- 
duce-itself as such; like produces like, though in this instance 
the like is in the first instance a departure from the normal. 
Gout is well known to be a hereditary disease; not only so, but 
it arises in the offspring at about the same age as in the parent, 
which is equivalent to saying that in the rhythmical life of 
