Ee 
TRANSACTIONS OF SECTION D. 765 
to the features of the machinery itself, and the words ‘acquired character’ to the 
results achieved by its working. These clearly will depend primarily on the 
structure of the machinery, and secondarily upon the material and energy supplied 
to it—that is to say, upon the way in which it is worked. 
Variations in genetic characters are variations in the machinery of different 
zygotes—that is to say, in the constitution—while variations in acquired characters 
are variations in the results of the working of one zygote according to the 
conditions under which it is worked. 
For instance, let us take the case of those twins which arise by the division of 
one zygote, and are consequently identical in genetic characters, 7.e. in constitution. 
If they are submitted to different conditions, they will develop differences which 
will depend entirely upon the conditions and the time of life when the differen- 
tiation in the conditions occurred. ‘These differences then will be a function of the 
external conditions, z7.e. of the manner in which the machinery is worked, and 
constitute what we call variation in acquired characters, 
Are Acquired Characters Transmissible as such in Reproduction ? 
To return to our question, are the so-called acquired characters ever trans- 
mitted in reproduction? Let us consider what this question means in the light of 
the preceding discussion. Acquired characters are features which arise in the 
zygote in response to external stimuli. Now the zygote at its first establishment 
has none of the characters which are subsequently acquired. All it has is the 
power of acquiring them. Clearly, then, acquired characters are not transmitted. 
The power of producing them is all that can be transmitted ; and this power resides 
in the reproductive organs and in the gametes to which the reproductive organs 
give rise, so that the question must be put in another form. Is it possible by 
submitting an organism to a certain set of conditions, and thus causing it to acquire 
certain characters, so to modify its reproductive organs that the same characters 
will appear in its offspring as the result of the application of a different and 
simpler stimulus ? 
For instance, the power of reading conferred by education, the hardness of the 
hands and increased size of the muscles produced by manual labour : is it possible 
that these characters, now produced by complex external stimuli applied at a 
particular period of life, should ever in future ages be produced by the simpler 
stimuli found within the uterus, so that a man may be born able to read or write, 
or with hands horny and hard like those of a navvy ? 
In trying to find an answer to this question let us first of all look into the 
probabilities of the case, to see if we can relate the question to any other class of 
phenomena about which we have, or think we have, definite knowledge. 
When an organism is affected by external agents the action may apply to the 
whole organisation or principally to one organ. Let us take a case in which one 
organ only appears to be affected, e.g. the enlargement by exercise of the right arm 
of a man. Now, although in this case it is only the muscles of the arm which 
appear at first sight to be affected, we must not forget that the organs of the body 
are correlated with one another, and an alteration of one will produce an altera- 
tion in others. By exercise of the right arm the muscles of that arm are obviously 
enlarged, but other changes not so obvious must also have taken place. The 
bones to which the muscles are attached will be altered; the blood-vessels sup- 
plying the muscles will be enlarged, and the nerves which act upon the muscles, 
and probably the part of the central nervous system from which they proceed, will 
also be altered. ‘These are some of the more obvious correlated changes which 
will have occurred ; no doubt there will have been others—indeed it is not perhaps 
too much to say that all the organs of the body will have reacted to the enlarge- 
ment of the arm—but the effect on organs not in functional correlation with the 
muscles of the right arm will be imperceptible, and may be neglected. Thus the 
colour of the hair, the length and character of the alimentary canal, size of the 
leg muscles, the renal organs, &c., will not show appreciable alteration. 
Above all, the other arm will not be affected, or if it is affected the alteration 
