744 ; The American Naturalist. [September, 
It is apparent that both of the last named writers, who have 
not themselves had a practical experience in collecting and 
studying cave animals and their surroundings, nor have care- 
fully read the recent literature on the subject, are overmastered 
by speculative views, and prefer to make an extremely vague, 
unscientific and a priori speculation, rather than adopt an 
opinion based on the inductive method. 
In refreshing contrast are the views of the veteran English 
philosopher, Mr. Herbert Spencer, who, like Darwin, fully ap- 
preciates the direct bearings of disuse as a fundamental factor, 
and, with his rare good sense and penetration, recognizes the 
probability of the active agency of the principle of the trans- 
mission of acquired characters in the origin of cave life. 
Indeed, in caves, deep holes or burrows, or in dark subter- 
ranean streams and wells, to which the blind are restricted, 
we have conditions very closely parallel to those which obtain 
in asylums for the deaf and dumb. The array of facts pre- 
sented by Professor A. Graham Bell and the danger which 
exists of the formation of a distinct deaf-mute variety of man- 
kind, and the suggestions which he offers as to the most prac- 
ticable way to arrest the further development of the incipient 
variety, all afford an interesting and striking parallel to the 
case of blind animals which are to be found living in caves 
and similar places. 
The cave fauna, as a whole, is composed of individuals, all 
existing under the same conditions, living in partial or total 
darkness, and with eyes either defective or absent. Now, how 
did they come there? We occasionally find, all over the 
world, creatures with defective sight or imperfectly-developed 
eyes, but such cases are sporadic, and are not numerous enough 
in proportion to the normal population to breed together and 
to multiply. Where, however, individuals with more or less 
defective eyes should breed with normal mates, any tendency 
to the transmission of such defects would be wiped out by the 
swamping effects of crossing, owing to the immense preponder- 
ance of normal, vigorous forms with perfect vision. The 
whole tendency in nature in the upper world of light is to 
weed out such sporadic, defective forms. But in limestone 
