Popular Science Monthly/Volume 56/February 1900/The Blind Fishes of North America



"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— PSM V56 D0488 Cave salamander of the mississippi valley.pngFig. 1.—The cave salamander of the Mississippi Valley (Spelerpes maculicauda). 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.

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 Cunha, 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 Schiifeldtii 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, PSM V56 D0489 The larva and adult of the missouri cave salamander.pngFig. 2.-The larva and adult of the Missouri cave salamander (Typhlotriton). 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:

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 papilliferns 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 subterranens 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. Trogliehthys rosge inhabits the caves west of the Mississippi in Arkansas and Missouri.

Chologaster.—Mr. E. B. Forbes secured a school of Chologaster papilliferns 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.

Chologaster papilliferus detects its food entirely by the sense of touch. Two which were kept in an aquarium for over a year

PSM V56 D0490 Blind salamander from an artesian well in texas.png
Fig. 3.—Blind salamander from an artesian well at San Marcos, Texas {Typhlomolge).

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

PSM V56 D0492 Ipnops murrayi and chlorophtalmus gracilis from the nz deep.png
Fig. 4.Ipnops Murrayi, living at a depth of 1,500 to 2,100 fathoms.
Fig. 5.Cholorophthalmus gracilis, from 1,100 fathoms, off New Zealand.

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. 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

PSM V56 D0493 Brodula barbata and sygicola dentatus from cuba.png
Fig. 6.—Brodula barbata from Havana, Cuba. Fig. 7.—Stygicola dentatus from the caves of Cuba.

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.

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

PSM V56 D0494 Seven deep ocean fishes.png
Fig. 8.—Aphyonus gelatinosius, 1,400 fathoms, between Australia and New Guinea.
Fig. 9.—Aphyonus mollis, 955 fathoms, 24° 36' north, 84° 5' west.
Fig. 10.—Tauredophidium hextli, 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.
Fig. 14.—Alexeterion parfaiti, 5,005 metres, North Atlantic.

fishes would starve in a cave river, where much of the food is carried to them on the surface of the stream."

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 Cœcidotæea 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[1] has suggested the same for Typhlogobius.

"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 PSM V56 D0496 Mancalias schufeldtii at 372 fathoms.pngFig. 15.—Mancalias Shufeldtii, 372 fathoms. to knit them together. There is, however, no pink coloration."

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

PSM V56 D0499 Typhlogobius and gillichthys mairabilis.png
Fig. 16.—The embryo of Typhlogobius, showing the well-developed eye.
Fig. 17.—A young Typhlogobius, times 429.
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.

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.

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.[2] 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.

  1. Ritter, Museum of Comparative Zoölogy, vol. xxiv, p. 92.
  2. 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.