1894.] Subterranean Fauna of North America. 747 
those with congenital variations breed together or intermarry, 
it is also to be taken for granted that it may, at times, be im- 
possible to draw the line between the transmission of congeni- 
tal and of acquired characters. 
When a number, few or many, of normal, seeing animals 
enter a totally dark cave or stream, some may become blind 
sooner than others; in others there may be developed only a 
tendency to blindness, the eye itself being imperceptibly mod- 
ified by disuse, while a certain percentage may possess the 
tendency plus a slight physical defect, either functional or 
organic, in the eyes, especially in the optic nerves and ganglia. 
The result of the union of such individuals and of adaptation 
to their stygian life would be broods of young, some with vis- 
ion unimpaired, others with a tendency to blindness, while in 
others there would be noticed the first steps in degeneration of 
nervous power and of nervous tissue. Even in a succeeding 
brood, or in a third brood, we might have a few individuals 
which were born blind or partly so, and were compelled to feel 
their way about the cave, while the far more numerous mem- 
bers of the colony would only exhibit a tendency to the disuse 
of their eyes, attempting to see their way rather than to feel it. 
Thus, after a few, or only several generations, the society of 
troglodytes, vertebrate and invertebrate, might be compared 
to a newly-established asylum of deaf mutes or to an asylum 
for the blind, if they interbred in the same proportions. 
At first, then, the number of cases of those not congenitally 
blind, but which, after living for most of their life time in 
darkness and becoming so modified that they could dispense 
with the use of their eyes, pari passu becoming more and more 
dependent on the exercise of their tactile organs—at first, such 
individuals as these would greatly preponderate. 
So all the while the process of adaptation going on, the an- 
tennae and other tactile organs increasing in length and in 
the delicacy of structure of their olfactory and tactile struc- 
tures, while the eyes were meanwhile diminishing in strength 
of vision and their nervous force giving out; after a few gen- 
erations, (perhaps, Judging by what we know of the sudden 
production of deaf mutes in human societies, only two or 
