THE OKIES OE HEREDITY. 
257 
Nov., 1889. 
Repair, and the renewal of lost parts in certain animals, 
is also explained by the persistence of the cells which were 
the immediate precursors of that part or tissue ;—cells which 
would be ready to pass through the last stages of develop¬ 
ment under the stimulus provided bv an injury. 
The simulicitv and beautv of Professor Weismamrs tlieorv 
of hereditv commends it to our favourable attention, and 
demands a searching enquiry into the evidence for the sun- 
posed transmission of acquired or somatogenic characters. 
Into this enquiry it is impossible to enter on the present 
occasion. I will onlv mention the various lines of evidence 
which require investigation. The evidence may be either 
Direct or Indirect. Direct proof would be afforded if an 
undoubtedlv somatogenic character could be shown to have 
reappeared in the offspring sufficiently often to prevent its 
explanation as a coincidence. Thus, if mutilations, or the 
pure results of training, exercise, or education (as apart from 
predisposition), or acquired diseases (many diseases are 
certainly blastogenic) reappeared in the offspring as the result 
of the operation of heredity, the required proof would be 
afforded and the theory of the continuity of tlie genn-plasm 
would collapse. Many diseases are due to living organisms 
(“ germs' 1 ), and when these reappear in the offspring the 
result is clearlv due to inoculation of the embrvo or even the 
€/ */ 
germ-cell (as in the silkworm disease), and is not therefore 
due to the operation of heredity. 
The present adverse position of the medical faculty is in 
part due to want of discrimination between blastogenic and 
somatogenic characters ; in part to the fact that the evidence 
on which they rely was collected when the transmission of 
somatogenic characters was assumed by everyone ; and in part 
to real difficulties which, however, require the most careful 
re-examination before they can be accepted as proofs of the 
transmission of acquired characters and as the death-blow to 
Weismann’s theory. 
If the Direct evidence for the transmission of acquired 
characters fails to stand the ordeal of a thorough investiga¬ 
tion, the Indirect evidence still remains. If it could be shown 
that certain phases of evolution would have been impossible 
without such transmission, we should be compelled to main¬ 
tain that the latter had taken place. 
The chief lines of Indirect evidence are :—The fact of 
individual variation, the effects of use and disuse of parts, 
the facts presented by the phenomena of instinct. 
