900 
into a normal frog, though it leads a purely 
vegetative life. Higher yet in the scale 
among birds and mammals, and most of all 
among the highest mammals, the animal 
attains its full development, as regards 
many structures, only in response to the 
stimulation of exercise and use; thus, for 
instance, if the limb of an infant be locked 
by paralysis or by a joint disease so that it 
cannot be used it does not develop into an 
adult limb. Now, if a ‘normal’ man takes 
a more than ordinary amount of exercise 
he gets a more than ordinary development 
of various structures, as happens in the 
ease of the blacksmith’s arm. This extra 
development is regarded by biologists as 
‘abnormal’ and is rightly termed ‘ ac- 
quired.’ But, as we see, the ‘normal’ de- 
gree of development is attained only as 
a response to exercise (1. e., stimulation), 
similar in kind though less in amount. 
Therefore, it is clear that the full development of 
the normal adult arm, as well as many other impor- 
tant structures, is acquired, differing in this 
from eyes, ears, teeth, nails, etc., which are 
wholly inborn, and do not owe their devel- 
opment in the least to use and exercise. 
In fact, on consideration, I think it will be 
found that adult man differs physically 
from the infant almost wholly in characters 
which are acquired, not in those which are 
inborn. In teeth, hair, skull-bones, gen- 
ital organs, and in some other respects, he 
differs from the infant as regards inborn 
characters; but as regards almost all the 
structures of the trunk and limbs, and 
most of those of the head, the difference is 
in characters which have been acquired by 
the adult as a response to the stimulation 
of exercise and use. ‘Thus the limbs de- 
velop wholly in response to use, the heart 
and arteries develop within certain limits 
in proportion to the strain put on them, as 
also do the lungs and their accessory mus- 
cles, as well as the bony attachments of the 
latter. The muscles, arteries, nerves, etc., 
SCIENCE. 
N.S. Von. VI. No. 155. 
of the head and neck also develop in re- . 
sponse to thesame stimulation. Moreover, 
the normal standard of development is 
maintained only as a response to this stim- 
ulation (7. ¢., use, exercise), for example, 
when not used, the muscles with their co- 
ordinated structures atrophy and tend to: 
disappear, as in the case of a paralyzed 
limb. It may be added that it is probable 
that even the infantile standard of de- 
velopment is, to some extent, acquired 
under the stimulus of foetal movements in 
utero. 
In upholding the doctrine of the trans- 
missibility of acquired modifications much 
stress has been laid by Mr. Herbert Spencer 
and others on the exquisite coordination of 
the multitudinous parts of the high animal 
organism. They maintain that this co- 
ordination affords decisive proof of the 
Lamarckian theory, the line of argument 
being as follows: Itis not probable that 
all the many structures of a high animal 
can ever have varied favorably together 
(as compared to the parent) in any indi- | 
vidual animal. Itis unbelievable that they 
can all have varied favorably generation 
after generation inalineof individuals. A 
chain is only as strong as its weakest link. 
A favorable variation, say a larger horn in 
the elk, if unaccompanied by correspond- 
ing variation in all the thousand parts (in 
head, neck, trunk, limbs) codrdinated with 
it, would be useless, and even burdensome. 
In other words, ifa single structure (muscle, 
bone, ligament, ete.) of all those associated 
with it failed to bear the strain of the 
Jarger horn, this variation would not favor 
survival, but, on the contrary, be a cause 
of elimination. Therefore, say these 
thinkers, the evolution of high multi- 
cellular animals cannot be attributed to the 
accumulation, during generations, of inborn 
variations alone, but must in part be at- 
tributed to the accumulation, during gene- 
rations, of the effects of use and disuse, 2. e., 
