1894.] Subterranean Fauna of North America. 199 
ously as soon as their ancestors took up a burrowing mode of 
life, they were prevented from crossing with others of their 
species, and, probably, when in sporadic cases it did occur, very 
soon the swamping effects of intercrossing wholly ceased, only 
those in which the eyes had begun to degenerate interbreed- 
ing. Aftera few generations, therefore, owing to this isolation, 
the partially blind forms became fixed by heredity and by the 
very force of circumstances a blind or eyeless generation re- 
sulted. 
These cireumstances are paralled by the results of the inter- 
marriage of deaf-mutes. Professor A. Graham Bell‘ has 
pointed out the danger of the establishment of a distinct 
variety of deaf-mutes with a special sign language of their 
own, since owing to their peculiar social environment and iso- 
lation in society there has lately arisen a strong tendency of 
deaf mutes to intermarry. The result, so far as gathered from 
a tolerably wide range of facts, shows that this incipient deaf 
mute strain or variety may have originated in two genera- 
tions, since it seems probable, as Mr. Bell remarks, “that the 
oldest deaf mute in the country whose parents were both deaf 
mutes is now only a little past middle age.” 
Moreover, the cases we have cited tend to show that the 
origination of new species and genera of subterranean, as well 
as deep sea forms and others living in darkness, may have 
been induced after comparatively few generations. Future 
observations should be directed to this point. The moment 
that several individuals became isolated in dark holes or in 
caves, and more or less confined in such narrow limits, the 
effects of darkness would at once begin to be experienced, and 
some degree of adaptation to their changed conditions would 
immediately begin to operate. The individuals of this gener- 
ation, i, e., the new comers in the cave, or those gobies which 
by burrowing in the mud had penetrated out of reach of their 
* On the formation of a deaf variety of the human race. Memoirs National 
Academy of Sciences for 1883, Washington, ii, 179-262, 1884. The author points 
out the means of isolation ot deaf mutes through asylums and national, state and 
city associations for 
He also gives “ specimen n cases to prove that in ‘many different parts of the coun- 
try deafness has been transmitted by heredity.” (p. 210). 
