“An investigation into the history of degenerate forms often
teaches us more of the causes of change in organic Nature than can
be learned by the study of the progressive ones.”--WEISMANN.
The caves of the United States are inhabited by three cave salamanders,
two of them with degenerate eyes; by six cave fishes, all with impaired
vision--five of them with rudimentary eyes, one with eyes the most
degenerate among vertebrates; and by several mammals. It is thus seen
that among the interesting features of the North American fauna the
blind vertebrates are not the least. Yet during the past twenty-five
years the only additions to our knowledge, aside from diagnoses of new
species, have been a few random notes on the habits and a short account
of the eye of Troglichthys by Kohl.
Various classes of vertebrates have blind members, but no large
vertebrate has become blind or permanently taken up its home in caves.
Blatchley reports that a number of cats have established themselves
in Wyandotte Cave, where they bring forth and rear their young. They
have exterminated the cave rats, and now station themselves in a narrow
passage of the cave and capture bats as they fly through.
Among the permanent residents in dark places we have, among mammals,
the moles, which habitually live in burrows of their own make. In
Mammoth Cave lives a rat--Neotoma pennsylvanica. In Marengo Cave,
Indiana, white-footed mice have established themselves. Although with
unimpaired eyes, they have acquired ears and whiskers longer than the
rest of their kind living outside.
In Florida occurs a blind lizard--Rhineura floridana. It burrows in the
ground, and is colorless and blind.
[Illustration: FIG. 1.--The cave salamander of the Mississippi Valley
(_Spelerpes maculicauda_).]
Of salamanders, one blind species lives in European caves. In the
large caves of the eastern United States no blind salamanders have
been found, although other species, especially Spelerpes maculicauda,
abound. In the caves of Missouri a veiled-eyed salamander,
Typhlotriton, has been described within recent years by Stejneger.
Still another salamander, Typhlomolge, having rudimentary eyes, has
been cast up from an artesian well at San Marcos, Texas, and occurs in
the cave streams about that place.
The most abundant of the blind vertebrates, both in individuals and
in species, are the blind fishes. These, from their geographical
distribution, may be separated into three groups: (1) Those inhabiting
the depths of the ocean; (2) those inhabiting dark places along the
shores of the ocean; (3) those inhabiting the underground fresh waters.
The fishes, blind or partially blind, living in the depths of the ocean
bordering the American continents, are as follows: 1. Ipnops Murrayi
Günther lives at depths varying from 955 fathoms to 2,158 and has the
very wide distribution suggested by the localities from which specimens
have been secured--viz., off the coast of Brazil, near Tristan da
Cumba, near Celebes, latitude 24° 36′ north, longitude 84° 51′ west,
and off Bequia. This is the only vertebrate in which no vestige of an
eye has been found. Ipnops stands alone in a family. 2. The Brotulidæ
have several members blind or with very much reduced eyes in various
parts of the globe. Aphyonus mollis G. and B., 955 fathoms, and
Alexeterion parfaiti Vaillant, 5,005 metres, are the only ones found
in the neighborhood of America. 3. The Lophiidæ are represented by
Mancalias Schufeldtii Gill, from a depth of 372 fathoms. Other blind
species are found in foreign waters, while others with small eyes
are found in American waters. The majority of deep-sea fishes have
well-developed eyes.
The shore fishes have their blind representative in Typhlogobius
californiensis St., which lives under rocks between tide water on the
coast of southern and Lower California. I have elsewhere described
the habits of this form. In the fresh-water caves of Cuba two blind
fishes--Stygicola denta Poey and Lucifuga subterraneus Poey--have been
found. Their relatives live in the ocean, Brotula barbata in Cuban
waters; some of the others are blind and inhabitants of deep water.
The inland fresh-water fishes are represented by Gronias nigrilabris
Cope, a catfish from cave streams of eastern Pennsylvania, and by
members of the Amblyopsidæ, concerning which a more detailed account is
given below.
THE AMBLYOPSIDÆ.--The Amblyopsidæ are a small family of fishes allied
to the Cyprinodontidæ. They are found in the Mississippi drainage
basin and in certain southeastern streams. Three of the members of
the family, the Chologasters, are provided with well-developed eyes,
while four other species are cave fishes in the strictest sense, being
blind and colorless. The distribution of the different members of the
Amblyopsidæ is as follows:
[Illustration: FIG. 2.--The larva and adult of the Missouri cave
salamander (_Typhlotriton_).]
Chologaster cornutus is found in lowland swamps of the Southern States
from the Dismal Swamp to the Okefinokee Swamp. Chologaster Agassizii is
found in subterranean streams in Tennessee and Kentucky. Chologaster
papilliferus has so far been found only in southwestern Illinois.
Amblyopsis is abundant in the cave streams of the Ohio Valley south of
the east fork of White River.
Typhlichthys subterraneus inhabits the region south of the Ohio and
east of the Mississippi. A single specimen of another Typhlichthys
has been found north of the Ohio River in a well at Corydon, Indiana.
Troglichthys rosæ inhabits the caves west of the Mississippi in
Arkansas and Missouri.
CHOLOGASTER.--Mr. E. B. Forbes secured a school of Chologaster
papilliferus for me, and he wrote: “The little fishes were found
under stones at the edges of the spring very close to the bluff, and
when disturbed they swam back under the cliff.... None were found at
any considerable distance from the face of the cliff.” I found the
Chologaster Agassizii to act similarly in the river Styx, in Mammoth
Cave. As soon as my net touched the water they darted in under the
ledge of rock at the side of the little pool in which I found them.
[Illustration: FIG. 3.--Blind salamander from an artesian well at San
Marcos, Texas (_Typhlomolge_).]
Chologaster papilliferus detects its food entirely by the sense of
touch. Two which were kept in an aquarium for over a year were starved
for a few days. They became very nervous, continually swimming along
the sides of the aquarium. Asellus was introduced. These, even if quite
near, produced no effect if moving in front of the Chologaster. The
moment one came in close proximity to the fish from any direction, by
a flashlike motion it was seized. None of them were swallowed. The
fish became very alert after the introduction of the sowbugs, and
when swimming forward would strike at a part of a leaf if it came in
contact with the head of the fish. It seemed evident that the eye
gave no information of the character of the object. As Asellus was
not altogether to their taste, Gammarus was introduced. One of these
swimming rapidly toward the chin of the Chologaster from behind and
below was instantly seized when it came in contact with the fish. The
eye could not have located the Gammarus at all. The action is in very
strong contrast to the action of a sunfish, which detects its food by
the sight. It is undoubtedly this peculiar method of locating and
securing food which has enabled the Amblyopsidæ to establish themselves
in caves.
The Chologaster in general make-up is like Amblyopsis, but is somewhat
longer-jointed. It sits with its pectorals extended. When it moves
horizontally for some distance the pectorals are usually pressed to the
sides, the propelling being done largely by the tail very much after
the manner of a salamander, which it resembles. In swimming toward the
surface it uses its pectoral fins chiefly, and the fish usually sinks
to the bottom as soon as its efforts to raise itself are stopped.
Individuals kept in aquaria with one end darkened either collected in
the darkened area floating about, or under leaves or sticks in any part
of the aquarium. They are frequently found under a floating board,
where they float with the tops of their heads in contact with the
board, their bodies slanting downward. They seek the dark, regardless
of the direction of the rays of light. These characteristics they
have, in great part, in common with the blind members of the family.
The adult Amblyopsis frequently floats with its head to the top of
the water, the tail sloping downward, and in swimming along ledges of
rock the top of the head is applied to the ledge. I have captured many
specimens simply by scraping my net along the surface of a ledge.
Typhlichthys, living in total darkness, has retained the habit of
staying under floating boards, sticks, and stones. Miss Hoppin noticed
that Troglichthys swims with its back to the sides of the aquarium, and
I have repeatedly noted the same in the young of Amblyopsis up to fifty
millimetres, and the still younger Amblyopsis frequently hides under
rocks.
AMBLYOPSIS.--The general impression given by Amblyopsis is that of
a skinned catfish swimming on its back. The expressions, “They are
catfish”; “They look as though they were skinned”; “They are swimming
on their backs,” are heard from those who see these fishes for the
first time.
The largest individual secured by me measured 135 millimetres in total
length. Individuals as large as this are rare. The usual length of an
adult is about 90 millimetres. One individual was mentioned to me at
Mammoth Cave having a length of 200 millimetres!
Amblyopsis is found in pools in the cave streams it inhabits. I have
secured as many as twelve from a pool perhaps ten by fifty feet in
size. Very rarely they are to be found in the riffles connecting the
pools. I have seen them lying at the bottom, or swimming, or rather
gliding, through the water like “white aquatic ghosts.” In the aquarium
they lie at the bottom or at various depths in the water, their axes
making various angles with the horizontal, their pectorals folded to
their sides. When swimming slowly it is chiefly by the use of the
pectorals. The strokes of the pectoral are lazily given, and the fish
glides on after a stroke till its impetus is exhausted, when another
stroke is delivered. The fishes frequently roll slightly from side
to side at the exhaustion of the result of a stroke. When swimming
rapidly the pectorals are folded to the sides, and their locomotion is
then similar to that of a salamander--by the motion of the tail. They
readily adjust themselves to different depths, and are usually perfect
philosophers, quiet, dignified, unconcerned, and imperturbed, entirely
different from such eyed species as minnows and sunfishes which are
sometimes found in caves and which are much more readily disturbed by
any motion in the water, making it almost impossible to capture them
when found in the caves. The pectorals are also almost exclusively
used when quietly rising in the water. At such times the pectorals are
extended laterally and then pressed to the sides, beginning with the
upper rays. A downward stroke is delivered in this way not quickly,
but with apparent lazy deliberation. In swimming the pectorals are
brought forward upper edge foremost. The center of gravity seems to
be so placed in regard to their various axes that the fish does not
lose its balance whatever its position. They float horizontally in the
water without any apparent effort to maintain their position, or with
the main axis inclined upward, with the snout sometimes touching the
surface of the water, apparently lifeless. Once one was seen resting on
its tail in a nearly vertical position, and one while quietly swimming
was once seen to leisurely turn a somersault and swim on undisturbed.
At another time the same individual rolled completely over. When one of
them is kept out of the water for a short time it frequently goes in a
corkscrew-shaped path through the water, continually spinning around
its long axis. In their quiet, floating position it is difficult to
determine whether they are alive or not.
[Illustration: FIG. 4.--_Ipnops Murrayi_, living at a depth of 1,500 to
2,100 fathoms.
FIG. 5.--_Chlorophthalmus gracilis_, from 1,100 fathoms, off New
Zealand.]
I have not found the slightest difficulty in capturing Amblyopsis
with a small dip net, either from a boat or while wading through the
subterranean stream, and I have caught one in the hollow of my hand.
At such a time all the noise I could make did not affect the fishes
found swimming in the water. Frequently they were taken in the dip net
without apparently noting the vibrations produced in the water until
they were lifted out of it; very rarely a fish became evidently scared.
Such a one would dart off a few feet or a few inches, and remain on
the _qui vive_. If not pursued, it soon swam off quietly; if pursued,
it not infrequently escaped by rapidly darting this way and that;
when jumping out of the water, often an abrupt turn in the opposite
direction from which it started would land it in the net, showing
that their sense of direction was not very acute. At other times, if
disturbed by the waves produced by wading, one or another individual
would follow a ledge of rock to the bottom of the stream, where it
would hide in a crevice. But very frequently, much more frequently than
not, no attention was paid either to the commotion produced by the
wading or by the boat and dip net. In general, it may be said that the
fishes in their natural habitat are oblivious to disturbances of the
water until frightened by some very unusual jar or motion, probably a
touch with the net, when they become intensely alert. The fact that
they are not easily frightened suggests the absence of many enemies,
while their frantic behavior if once scared gives evidence either that
occasional enemies are present and that they are very dangerous, or
that the transmission of the instinct of fear is as tenacious as the
transmission of physical characters.
[Illustration: FIG. 6.--_Brodula barbata_ from Havana, Cuba.]
[Illustration: FIG. 7.--_Stygicola dentatus_ from the caves of Cuba.]
Contrary to Sloan’s observation, that they detect the presence of a
solid substance in their path, I have never noticed that those in
confinement became aware of the proximity of the walls of the aquarium
when swimming toward it. Instead, they constantly use the padded,
projecting lower jaw as bumpers. Even an extremely rapid dart through
the water seems to be stopped without serious inconvenience by the
projecting jaw.
The first observations on the feeding habit of Amblyopsis are those of
Cope. He remarks that “the projecting lower jaw and upward direction
of the mouth render it easy for the fish to feed at the surface of the
water, where it must obtain much of its food.... This structure also
probably explains the facts of its being the sole representative of the
fishes in subterranean waters. No doubt many other forms were carried
into the caverns since the waters first found their way there, but most
of them were like those of our present rivers--deep-water or bottom
feeders. Such fishes would starve in a cave river, where much of the
food is carried to them on the surface of the stream.”
[Illustration: FIG. 8.--_Aphyonus gelatinosus_, 1,400 fathoms, between
Australia and New Guinea.
FIG. 9.--_Aphyonus mollis_, 955 fathoms, 24° 36′ north, 84° 5′ west.
FIG. 10.--_Tauredophidium hextii_, 1,310 fathoms, Bay of Bengal.
FIG. 11.--_Acanthonus armatus_, 1,050 fathoms, mid Pacific, off the
Philippines.
FIG. 12.--_Typhlonus nasus_, 2,150 to 2,440 fathoms, north of Australia
and north of Celebes.
FIG. 13.--_Hephthacara simum_, 902 fathoms, Coromandel coast.