The observations of Cope are entirely erroneous, as we shall see, and
the speculations based on them naturally fall to the ground.
Dr. Sloan recorded one Amblyopsis which he kept twenty months without
food. “Some of them would strike eagerly at any small body thrown in
the water near them, rarely missed it, and in a very short time ejected
it from their mouths with considerable force. I tried to feed them
often with bits of meat and fish-worms, but they retained nothing. On
one occasion I missed a small one, and found his tail projecting from
the mouth of a larger one.”
Wyman found a small-eyed fish in the stomach of an Amblyopsis.
Hoppin was struck by the fact that, if not capable of long fasts,
Troglichthys must live on very small organisms that the unaided eye can
not discern. Garman found, in the stomachs of Troglichthys collected
by Hoppin in Missouri, species of Asellus, Cambarus, Ceuthophilus, and
Crangonyx.
All the specimens of Amblyopsis so far taken by me contained very
large fatty bodies in their abdominal cavity, a condition suggesting
abundance of food. The stomachs always contained the _débris_ of
crustaceans, a closer identification of which was not attempted. One
young Amblyopsis disappeared on the way home from the caves, and had
evidently been swallowed by one of the larger ones. A few old ones,
kept in an aquarium from May to July, were seen voiding excrement
toward the last of their captivity, and their actions at various
times suggested that they were scraping the minute organisms from the
side of the aquarium. The young Amblyopsis reared in the aquarium
seemed to feed on the minute forms found in the mud at the bottom
of its aquarium. Some Cœcidotæa placed in the aquarium of the young
soon disappeared, and the capture of one of these was noted under a
reading glass. The fish was quietly swimming along the side of its
aquarium; when it came within about an inch of the crustacean it became
alert, and with the next move of the Cœcidotæa it was captured with
a very quick, well-aimed dart on the part of the young fish. Others
were captured while crawling along the floor of the aquarium. From
all things noted, it seems very probable that Amblyopsis is a bottom
feeder, and that it also picks food from the walls of the caves. It is
not at all improbable or impossible that food should be captured at
the surface or in open water, but there seems no warrant for Cope’s
supposition that Amblyopsis is a top feeder. I have frequently seen
larger specimens, which had been in captivity for several weeks, nosing
about the bottom of the aquarium, with their bodies inclined upward in
the water and quietly taking in the organic fragments at the bottom.
An Asellus stirring about at such a time always produced an unusual
alertness.
The number of respiratory movements of Amblyopsis averaged nineteen a
minute in five observations, reaching a maximum of thirty in a small
individual and a minimum of fourteen in a large one. This is in strong
contrast to Chologaster, the number of whose respiratory motions
reached an average of eighty per minute in five observations, with
a minimum of fifty-six and a maximum of one hundred and eight in a
small specimen. Dr. Loeb has called my attention to the more rapid
absorption of oxygen in the light than in the dark; this extended would
probably mean the more rapid absorption of oxygen through the skin of
light-colored animals, a matter of doubtful value, however, to species
living in the dark.
The gill filaments are small as compared with the gill cavity.
Oxygenation probably takes place through the skin. Ritter[J] has
suggested the same for Typhlogobius.
[J] Ritter, Museum of Comparative Zoölogy, vol. xxiv, p. 92.
“Cutaneous respiration is not unique in Typhlogobius and the
Amblyopsidæ. In the viviparous fishes of California the general
surface, and especially the fins, which have become enormously
enlarged, serve as respiratory organs during the middle and later
periods of gestation; the fins are a mass of blood-vessels, with merely
sufficient cellular substance to knit them together. There is, however,
no pink coloration.”
[Illustration: FIG. 15.--_Mancalias Schufeldtii_, 372 fathoms.]
Skin respiration would account for the extreme resistance to
asphyxiation in Amblyopsis and Typhlogobius. About forty-five
examples of Amblyopsis were carried in a pail of water four hundred
miles by rail, with only a partial change of water three times
during twenty-four hours. A smaller number may be kept for days or
weeks--probably indefinitely--in a pail of water without change. The
characteristics of Typhlogobius along this line have been set forth
elsewhere.
Sticks, straws, etc., are never avoided by the fishes even when
perfectly imperturbed. By this I mean that they are never seen to avoid
such an object when it is in their path. They swim against it and then
turn. An object falling through the water does not disturb them, even
if it falls on them. A pencil gently moved about in front of them does
not disturb the fishes much, but if the pencil is held firmly in the
hand it is always perceived, and the fish comes to a dead halt ten or
fifteen millimetres before it reaches such an object. On the other
hand, they may be touched on the back or tail before they start away.
They glide by each other leisurely and dignified, and if they collide,
as they sometimes do, they usually show no more emotion than when they
run against a stick. But this indifference is not always displayed, as
we shall see under the head of breeding habits.
A number kept in an aquarium with a median partition, in which there
was a small opening, were readily able to perceive the opening,
swimming directly for it when opposite it. This observation is in
direct contrast to their inability to perceive solid substances in
their path. A sharp tap on the sides of an aquarium in which six
blind fishes were swimming, where they had been for a number of days
undisturbed, in a dark room, caused nearly all of them to dart rapidly
forward. A second tap produced a less unanimous reaction. This repeated
on successive days always brought responses from some of the inmates
of the aquarium. Those responding were not necessarily the nearest to
the center of disturbance, but sometimes at the opposite side of the
aquarium or variously distributed through it. After a few days the
fishes took no notice of the tapping by any action observable in the
artificially lighted room.
Such tapping on a well-lighted aquarium containing both Chologaster
and Amblyopsis was always perceived by the Amblyopsis, but the only
response from these imperturbable philosophers was a slight motion of
the pectorals, a motion that suggested that their balance had been
disturbed and that the motion was a rebalancing. Chologaster, on the
other hand, invariably darted about in a frantic manner. One individual
of Amblyopsis floating on the water was repeatedly pushed down by the
finger without being disturbed. If, however, they are touched on the
side they always rapidly dart away.
From everything observed, it is quite evident that Amblyopsis is not
keener in perceiving objects or vibrations than other fishes, and
ordinarily pays much less attention to them. Whether it possesses a
greater power of discrimination of vibrations it would be difficult to
say. It certainly possesses very elaborate tactile organs about the
head. These tactile organs are probably more serviceable in detecting
and precisely locating prey in the immediate neighborhood than for
anything else. Some observations on young Amblyopsis are of interest in
this connection.
The young, with a large amount of yolk still attached, show a
well-developed sense of direction. A needle thrust into the water near
their heads and in front of them causes a quick reaction, the young
fishes turning and swimming in the opposite direction. They will do
this two or three times, then, becoming exhausted, will remain at rest.
Sometimes an individual will not move until it is actually touched by
the needle. The needle must come within about three or four millimetres
of the fish before it is noticed. Then, if it produces any result, it
causes the fish to quickly turn and swim some distance, when it falls
to the bottom again and remains at rest. If the needle is placed
behind the fish, it will swim directly forward; if at the side or about
the middle, it causes the fish to swim directly forward or to turn and
swim in a direction opposite the origin of the disturbance. Younger
specimens have, as yet, no power over the direction of their progress;
the wiggling of the tail simply produces a gyration, with the yolk as
pivot.
A young blind fish, six months old, swims about in a jerky manner,
chiefly by the use of its pectoral fins. It keeps close to the side
of the vessel, usually with its back to the glass. (The aquarium was
a cylindrical jar three hundred millimetres in diameter and three
hundred millimetres high.) It perceives a stick thrust toward it
as readily as a seeing fish can. It always perceives from whatever
direction it may be approached, and will invariably dart away a short
distance, sometimes making sharp turns to avoid the stick, and always
successfully. It can be approached from the top nearer than from the
sides or from in front. It does not avoid the sides of the aquarium,
which it frequently strikes. It is a bottom feeder; its intestinal
canal is always partially full.
A long series of experiments was made on Amblyopsis and Chologaster
to determine their reaction to white and monochromatic light. Without
going into the details of these experiments, it may be stated that
Amblyopsis avoids the light, regardless of the direction or the color
of the rays. The same is true of Chologaster, except that they were
positively attracted by the red rays of the spectrum as against the
blue.
We owe the first observations on the breeding habits of Amblyopsis to
Thompson, who states that a fish “was put in water as soon as captured,
where it gave birth to nearly twenty young, which swam about for some
time, but soon died; ... they were each four lines in length.” Little
or nothing has been added to our knowledge of this subject since that
time, but the highly interesting supposition of Thompson that they were
viviparous has gained currency, and it is therefore unfortunate that in
this respect he was in error.
Putnam adds to the above that, judging from some data in his
possession, the young are born in September and October, and further
along remarks that they are “undoubtedly” viviparous.
The eggs are laid by the female in under her gill membrane. Here they
remain for perhaps two months, till the yolk is nearly all absorbed.
If a female with young in her gill pouches is handled, some of the
young are sure to escape. This was observed, and gave rise to the idea
that this fish is viviparous. Eggs have been obtained as early as
March 11th and as late as September, and the indications are that the
breeding season extends throughout the year. The eggs are large--2.3
millimetres in diameter from membrane to membrane--and about sixty to
seventy are laid at one time.
Certain structures gain an entirely new significance in the light of
the breeding habits. These are the enlarged gill cavities, with the
small gills, the closely applied branchiostegal membrane, and the
position of the anus and sexual orifices. The latter are placed just
behind the gill membrane in such close proximity to it that they can
be covered by it. It is probable, therefore, that the membrane is
drawn over the sexual orifice and the eggs deposited directly into the
gill cavity. In an individual thirty-five millimetres long the anus
is situated between the origin of the pectorals; in one twenty-five
millimetres long it lies between the pectorals and ventrals. In the
young it lies behind the ventrals, as in other fishes.
[Illustration: FIG. 16.--The embryo of _Typhlogobius_, showing the
well-developed eye.
FIG. 17.--A young _Typhlogobius_, times 4-2/9.
FIG. 18.--Adult _Typhlogobius_.
FIG. 19.--Adult _Gillichthys-y-cauda_ living in crab holes in San Diego
Bay.
FIG. 20.--Young _Gillichthys mirabilis_ under the same magnification as
Fig. 17.]
In an aquarium containing six Amblyopsis two took a great antipathy to
each other. Whenever they touched, a vigorous contest began. Frequently
they came to have a position with broadside to broadside, their heads
pointing in opposite directions. At such a time the fight consists
in quick lateral thrusts toward the antagonist to seize him with
the mouth. The motion is instantly parried by a similar move by the
antagonist. This blind punching may be kept up for a few seconds, when,
by their vigorous motions, they lose each other and jerk themselves
through the water from side to side, apparently hunting for each
other. At this time they are very agile, and move with precision. When
the belligerents meet one above the other, the snapping and punching is
of a different order. While jerking through the water immediately after
a round, if one of the belligerents touches one of the neutrals in the
aquarium it frequently gives it a punch, but does not follow it up, and
the unoffending fellow makes haste to get out of the road, the smaller
ones doing so most quickly. If, after an interval of a few seconds, a
belligerent meets a neutral they quietly pass each other without paying
any further attention, whereas if the two belligerents meet again there
is an immediate response. Whether they recognize each other by touch
or by their mutual excitability I do not know. At one time, in another
aquarium, I saw one belligerent capture the other by the pectorals.
After holding on for a short time it let go, and all differences were
forgotten. The thrust is delivered by a single vigorous flip of the
tail and caudal to one side. These fights were frequently noticed, and
always occurred between males.
The absence of secondary sexual differences in the cave fishes is a
forcible argument in favor of sexual selection as the factor producing
high coloration in the males. The absence of secondary sexual
differences in cave animals opposes the idea of Geddes and Thompson
that the differences are the external expression of maleness and
femaleness.
Attempts at acclimating Amblyopsis in outside waters have so far
failed.[K] A few were placed in Turkey Lake, Indiana. They were
surrounded by a fine wire net, to keep off other fishes. They died in
a few days, as the result of attacks of leeches, _saprolegnia_, or
fish mold, and from unknown causes. Others were kept in an elongated
box sunk into the ground, where fresh spring water flowed through it
constantly. _Saprolegnia_ sooner or later destroyed all of them. They
live longest in quiet aquaria, where the water is rarely changed. The
young I have secured died, with one exception, within a few weeks. The
difficulty of rearing the young is not at all insurmountable. They eat
readily. Their aquaria must be kept free from green plants, and have a
layer of fine mud, with a few decaying leaves, in the bottom. They will
feed on minute crustaceans and other micro-organisms. When they have
reached a sufficient size, examples of Asellus are greedily devoured.
Fish mold is the bane of the larvæ. Many of them were found with tufts
of the _hyphæ_ growing out of their mouths and gill openings.
[K] Since the above was written an apparently successful
attempt has been made to colonize them in a pool at Winona
Lake. A record of this colony will be published later.