746 The American Naturalist. [September, 
living in dark wells or subterranean streams, which have a 
more or less direct connection with the upper world. 
As regards the problem of the transmission of acquired char- 
acters, it would appear that the case with cave animals is 
paralled by that of deaf mutes collected together in asylums, 
and united by various social organizations. It has been 
shown in a striking way by Mr. Turner, as quoted by Bell, 
that “ before the deaf and dumb were educated, comparatively 
few of them married.” Bell concludes, from an examination 
of the records of deaf mute asylums in the United States, 
“that of the deaf mutes who marry at the present time, not 
less than 80 per cent marry deaf mutes, while of those who 
married during the early half of the present century the pro- 
portion who married deaf mutes was much smaller.” 
It was also clearly indicated that “a hereditary tendency 
towards deafness, as indicated by the possession of deaf rela- 
tives, is a most important element in determining the produc- 
tion of deaf offspring,” and “ it may even be a more important 
element than the mere fact of congenital deafness in one or 
both of the parents.” 
It appears, then, that it is the segregation of deaf mutes, in- 
including nearly half of the deaf mutes who became deaf from 
accidental causes, which has led to the apparent increase of this 
incipient strain or breed of human beings. And the statistics 
and conclusions given by Mr. Bell appear to almost demon- 
strate the fact of the transmission of characters acquired dur- 
ing the lifetime of the individual, and that it is difficult to 
draw the line between this phenomenon and the transmission 
of congenital characters; the latter being, at present, the more 
frequent and therefore normal law of heredity, though it was 
not so in the beginning. For, as Bell, after a careful study of 
statistics, remarks, “ The numbers of the non-congenitally deaf 
are evidently subject to great and sudden fluctuations on ac- 
count of the epidemical diseases which cause deafness, whereas, 
the growth of the congenitally-deaf population seems to be 
much more regular.” 
Premising that heredity does not, at the best, always uner- 
ringly act, that its results are sometimes uncertain, even where 
