130 The American Naturalist. [February, 
THE SIGNIFICANCE OF ANOMALIES: 
By Tuomas Dwiaeut, M. D., LL. D? 
This subject, which after consultation has been chosen for 
our discussion this year, is one which for a long time has in- 
terested and puzzled me extremely. I look forward with 
great pleasure to the light which I hope will be thrown upon 
it by distinguished members of this Association. For my part 
I propose merely to state some of the difficulties which it seems 
to present and suggest one or two general conclusions which 
seem to me to be justified. 
Probably no biological phenomena have been more con- 
fidently explained by heredity and atavism than rudimentary 
organs and anomalies. The former, of constant occurrence, 
though perhaps of transitory existence, have been happily 
compared by Darwin to letters in words which are no longer 
sounded, but which were pronounced at an earlier stage of the 
language. 
Anomalies are the occasional appearance of structures 
normal in other animals. That these are found very com- 
monly in man everyone knows. Whether they are found 
equally commonly in animals is a matter of uncertainty. Mr. 
Dobson believes that man as the type of a domesticated animal 
is particularly liable to them and that in wild animals they 
are extremely uncommon. ‘To this may be opposed the great 
frequency of anomalies in negroes. If I am not mistaken, 
other rebutting evidence is furnished by comparative anatomy. 
_ The same explanation has held for these; but as their grad- 
ually increasing numbers have brought more accurate study, 
serious difficulties have arisen. It is clear that if an anomaly 
in man is to be called a reversion, either the species in which 
it is normal must have been in the direct line of ancestry, or 
there must have been a common progenitor. Evident as this 
1Read at the meeting of the Association in New York on December 29th, 1894, to 
open the discussion. 
*President of the Association of American Anatomists. 
