in the Development of the System of Animal Life. 249 
But have other peculiarities of the later species any connection 
with this growth and change of brain? We can hardly doubt, 
that, inasmuch as there has been no corresponding change in the 
animal's bulk, there must have been concordant changes some- 
It is the means in an animal by which communication is had 
with the outer world and also with its own inner workings and 
appetites; that which takes impressions, which feels whatever 
inspires energy, prompts to action, exhilarates, or exalts; the 
part, therefore, which must grow whenever circumstances favor 
progress, and, at the same time, fail to grow or dwindle under 
unfavorable circumstances; which communicates whatever it 
the part or parts responding to its condition; which reaches 
every part of the system and dominates in all action and growth, 
and hence must cause an expression of its own condition in 
some way on the structure; which, moreover, must ordinarily 
produce correlate changes in correlated parts, if any, because in 
its Own nature and distribution the system of correlation has a 
full expression, Energetic use gives increasing strength to 
muscle ; and that wonderful strengthening growth in the brain 
since Kocene times may also have come from use. 
t would hence appear that a prominent means of change in 
Species is the action of influences on the brain; that the brain 
grows and changes and sends its changing forces through the 
animal; and that this gives progress, or degradation : and hence 
itis that progress is exhibited in cephalization, and degradation 
A “Peephalization. The brain could not grow to the adult stage 
In the rog without the change in the structure that cotempora- 
neously takes place; and no more could the brain of a species 
<¢ashrimp grow into a brain of the higher grade of a crab 
Without its determining in some sense a concordant higher 
grade of structure in the animal, involving the loss of locomo- 
tion e the abdomen and also other changes. beg co bl 
© recognize, as evidence of upward progress 1n Man, 3 
creasing bot’ width and Seatac bi: the forehead, and a 
