44 Relation of Animal Motion to Animal Evolution. (January, 
plants; or the new parts may differ from the old, as in higher 
animals, where the process is called “ modified repetition.” Where 
new forms traverse in their growth all the stages in which they | 
previously existed, they necessarily present at each stage the char- 
acters of those forms which have remained stationary in them, and 
have not changed. This relation of “exact parallelism” is the 
result of the simplest form of evolution or “palingenesis.” When 
the history of growth of an advanced form does not show an 
identity between its stages and the various undeveloped or lower 
adult types, the relation is termed “ inexact parallelism,” and the 
type of development “ccenogenesis.” 
Change of structure is seen to take place in accordance with 
the mechanical effect of three forms of motion, viz: by friction, 
pressure and strain. Under the first two, epidermal tissues be- 
come both dense and thick, as is seen on the’ palms and soles of 
the hands and feet and in corns. There is no doubt that strength 
of the teeth is intimately connected with the hardness of the 
food. Density of osseous tissue and the coossification of parts 
of the skeleton, are directly associated with the force and dura- 
tion of muscular contraction. Pathology abounds in illustrations 
of the determination of nutrition to new localities to meet the 
exigencies and demands arising from new stimuli. It is only 
necessary for a structure-producing supply of nutritive material 
to be habitually determined to a new locality by oft recurring 
stimulus, for the movement to become automatic and reflex ; and 
such a tendency would sooner or later be inherited, and produce 
structure in the growing organism of the young to a degree far 
exceeding anything that is possible in the adult. : 
In view of the above considerations, we can ascribe an exten- 
sive class of osseous projections at points of muscular insertion, 
to the strength and duration of muscular contractions. To the — 
_ Same cause may be ascribed various anchyloses, such for instance, 
= asis seen in the foot of the sloth. Transverse strains or theif 
absence may be looked upon respectively as the cause of the hinge- ` 
like or immoveable articulations of the segments of the limbs of — 
vertebrate animals. It is well known that in land animals, where 
easy flexibility of the limbs is essential to speed, that these articu- 
lations are highly developed, while in marine animals where the 
_ limbs are only used as paddles, they are almost or quite inflexible, a | 
and the extremities of the bones are truncate. Inthe most highly 7 
_ organized land mammalia, the tibio-tarsal, and humero-cubital — 
