CHAPTER XXVIII

THE CYCLOSTOMES, OR LAMPREYS

=The Lampreys.=--Passing upward from the lancelets and setting aside the descending series of Tunicates, we have a long step indeed to the next class of fish-like vertebrates. During the period this great gap represents in time we have the development of brain, skull, heart, and other differentiated organs replacing the simple structures found in the lancelet.

The presence of brain without limbs and without coat-of-mail distinguishes the class of _Cyclostomes_, or lampreys (~kuklos~, round; ~stoma~, mouth). This group is also known as _Marsipobranchi_ (~marsipion~, pouch; ~branchos~, gill); _Dermopteri_ (~derma~, skin; ~pteron~, fin); and _Myzontes_ (~myzaô~, to suck). It includes the forms known as lampreys, slime-eels, and hagfishes.

=Structure of the Lamprey.=--Comparing a Cyclostome with a lancelet we may see many evidences of specialization in structure. The Cyclostome has a distinct head with a cranium formed of a continuous body of cartilage modified to contain a fish-like brain, a cartilaginous skeleton of which the cranium is evidently a differentiated part. The vertebræ are undeveloped, the notochord being surrounded by its membranes, without bony or cartilaginous segments. The gills have the form of fixed sacs, six to fourteen in number, on each side, arranged in a cartilaginous structure known as "branchial basket" (fig. 289_a_), the elements of which are not clearly homologous with the gill-arches of the true fishes. Fish-like eyes are developed on the sides of the head. There is a median nostril associated with a pituitary pouch, which pierces the skull floor. An ear-capsule is developed. The brain is composed of paired ganglia in general appearance resembling the brain of the true fish, but the detailed homology of its different parts offers considerable uncertainty. The heart is modified to form two pulsating cavities, auricle and ventricle. The folds of the dorsal and anal fins are distinct, supported by slender rays.

The mouth is a roundish disk, with rasping teeth over its surface and with sharper and stronger teeth on the tongue. The intestine is straight and simple. The kidney is represented by a highly primitive pronephros and no trace exists of an air-bladder or lung. The skin is smooth and naked, sometimes secreting an excessive quantity of slime.

From the true fishes the Cyclostomes differ in the total absence of limbs and of shoulder and pelvic girdles, as well as of jaws. It has been thought by some writers that the limbs were ancestrally present and lost through degeneration, as in the eels. Dr. Ayers, following Huxley, finds evidence of the ancestral existence of a lower jaw. The majority of observers, however, regard the absence of limbs and jaws in Cyclostomes as a primitive character, although numerous other features of the modern hagfish and lamprey may have resulted from degeneration. There is no clear evidence that the class of Cyclostomes, as now known to us, has any great antiquity, and its members may be all degenerate offshoots from types of greater complexity of structure.

=Supposed Extinct Cyclostomes.=--No species belonging to the class of Cyclostomes has been found fossil. We may reason theoretically that the earliest fish-like forms were acraniate or lancelet-like, and that lamprey-like forms would naturally follow these, but this view cannot be substantiated from the fossils. Lancelets have no hard parts whatever, and could probably leave no trace in any sedimentary deposit. The lampreys stand between lancelets and sharks. Their teeth and fins at least might occasionally be preserved in the rocks, but no structures certainly known to be such have yet been recognized. It is however reasonably certain that the modern lamprey and hagfish are descendants, doubtless degraded and otherwise modified from species which filled the gap between the earliest chordate animals and the jaw-bearing sharks.

=Conodontes.=--Certain structures found as fossils have been from time to time regarded as Cyclostomes, but in all such cases there is doubt as to the real nature of the fossil relic in question or as to the proper interpretation of its relationship.

Thus the _Conodontes_ of the Cambrian, Silurian, and Devonian have been regarded as lingual teeth of extinct Cyclostomes. The _Cycliæ_ of the Devonian have been considered as minute lampreys, although the vertebral segments are highly specialized, to a degree far beyond the condition seen in the lampreys of to-day. The Ostracophores have been regarded as monstrous lampreys in coat of mail, and the possibility of a lamprey origin even for Arthrodires has been suggested. The _Cycliæ_ and _Ostracophori_ were apparently without jaws or limbs, being in this regard like the _Cyclostomes_, but their ancestry and relationships are wholly problematical.

The nature of the Conodontes is still uncertain. In form they resemble teeth, but their structure is different from that of the teeth of any fishes, agreeing with that of the teeth of annelid worms. Some have compared them to the armature of Trilobites. Some fifteen nominal genera are described by Pander in Russia, and by Hinde about Lake Erie and Lake Ontario. Some of these, as _Drepaniodus_, are simple, straight or curved grooved teeth or tooth-like structures; others, as _Prioniodus_, have numerous smaller teeth or denticles at the base of the larger one.

=Orders of Cyclostomes.=--The known Cyclostomes are naturally divided into two orders, the _Hyperotreta_, or hagfishes, and the _Hyperoartia_, or lampreys. These two orders are very distinct from each other. While the two groups agree in the general form of the body, they differ in almost every detail, and there is much pertinence in Lankester's suggestions that each should stand as a separate class. The ancestral forms of each, as well as the intervening types if such ever existed, are left unrecorded in the rocks.

=The Hyperotreta, or Hagfishes.=--The _Hyperotreta_ (~hyperôa~, palate; ~tretos~, perforate), or hagfishes, have the nostril highly developed, a tube-like cylinder with cartilaginous rings penetrating the palate. In these the eyes are little developed and the species are parasitic on other fishes. In _Polistotrema stouti_, the hagfish of the coast of California, is parasitic on large fishes, rockfishes, or flounders. It usually fastens itself at the throat or isthmus of its host and sometimes at the eyes. Thence it works very rapidly to the inside of the body. It there devours all the muscular part of the fish without breaking the skin or the peritoneum, leaving the fish a living hulk of head, skin, and bones. It is especially destructive to fishes taken in gill-nets. The voracity of the Chilean species _Polistotrema dombeyi_ is equally remarkable. Dr. Federico T. Delfin finds that in seven hours a hagfish of this species will devour eighteen times its own weight of fish-flesh. The intestinal canal is a simple tube, through which most of the food passes undigested. The eggs are large, each in a yellowish horny case, at one end of which are barbed threads by which they cling together and to kelp or other objects. In the California hagfish, _Polistotrema stouti_, great numbers of these eggs have been found in the stomachs of the males.

Similar habits are possessed by all the species in the two families, _Myxinidæ_ and _Eptatretidæ_. In the _Myxinidæ_ the gill-openings are apparently single on each side, the six gills being internal and leading by six separate ducts to each of the six branchial sacs. The skin is excessively slimy, the extensible tongue is armed with two cone-like series of strong teeth. About the mouth are eight barbels.

Of _Myxine_, numerous species are known--_Myxine glutinosa_, in the north of Europe; _Myxine limosa_, of the West Atlantic; _Myxine australis_, and several others about Cape Horn, and _Myxine garmani_ in Japan. All live in deep waters and none have been fully studied. It has been claimed that the hagfish is male when young, many individuals gradually changing to female, but this conclusion lacks verification and is doubtless without foundation.

In the _Eptatretidæ_ the gill-openings, six to fourteen in number, are externally separate, each with its own branchial sac as in the lampreys.

The species of the genus _Eptatretus_ (_Bdellostoma_, _Heptatrema_, and _Homea_, all later names for the same group) are found only in the Pacific, in California, Chile, Patagonia, South Africa, and Japan. In general appearance and habits these agree with the species of _Myxine_. The species with ten to fourteen gill-openings (_dombeyi_: _stouti_) are sometimes set off as a distinct genus (_Polistotrema_), but in other regards the species differ little, and frequent individual variations occur. _Eptatretus burgeri_ is found in Japan and _Eptatretus forsteri_ in Australia.

=The Hyperoartia, or Lampreys.=--In the order _Hyperoartia_, or lampreys, the single nostril is a blind sac which does not penetrate the palate. The seven gill-openings lead each to a separate sac, the skin is not especially covered with mucus, the eyes are well developed in the adult, and the mouth is a round disk armed with rasp-like teeth, the comb-like teeth on the tongue being less developed than in the hagfishes. The intestine in the lampreys has a spiral valve. The eggs are small and are usually laid in brooks away from the sea, and in most cases the adult lamprey dies after spawning. According to Thoreau, "it is thought by fishermen that they never return, but waste away and die, clinging to rocks and stumps of trees for an indefinite period, a tragic feature in the scenery of the river-bottoms worthy to be remembered with Shakespeare's description of the sea-floor." This account is not far from the truth, as recent studies have shown.

The lampreys of the northern regions constitute the family of _Petromyzonidæ_. The larger species (_Petromyzon_, _Entosphenus_) live in the sea, ascending rivers to spawn, and often becoming land-locked and reduced in size by living in rivers only. Such land-locked marine lampreys (_Petromyzon marinus unicolor_) breed in Cayuga Lake and other lakes in New York. The marine forms reach a length of three feet. Smaller lampreys of other genera six inches to eighteen inches in length remain all their lives in the rivers, ascending the little brooks in the spring, clinging to stones and clods of earth till their eggs are deposited. These are found throughout northern Europe, northern Asia, and the colder parts of North America, belonging to the genera _Lampetra_ and _Ichthyomyzon_. Other and more aberrant genera from Chile and Australia are _Geotria_ and _Mordacia_, the latter forming a distinct family, _Mordaciidæ_. In _Geotria_, a large and peculiar gular pouch is developed at the throat. In _Macrophthalmia_ _chilensis_ from Chile the eyes are large and conspicuous.

=Food of Lampreys.=--The lampreys feed on the blood and flesh of fishes. They attach themselves to the sides of the various species, rasp off the flesh with their teeth, sucking the blood till the fish weakens and dies. Preparations made by students of Professor Jacob Reighard in the University of Michigan show clearly that the lamprey stomach contains muscular tissue as well as the blood of fishes. The river species do a great deal of mischief, a fact which has been the subject of a valuable investigation by Professor H. A. Surface, who has also considered the methods available for their destruction. The flesh of the lamprey is wholesome, and the larger species, especially the great sea lamprey of the Atlantic, _Petromyzon marinus_, are valued as food. The small species, according to Prof. Gage, never feed on fishes.

=Metamorphosis of Lampreys.=--All lampreys, so far as known, pass through a distinct metamorphosis. The young, known as the _Ammocoetes_ form, are slender, eyeless, and with the mouth narrow and toothless. From Professor Surface's paper on "The Removal of Lampreys from the Interior Waters of New York" we have the following extracts (slightly condensed):

"In the latter part of the fall the young lampreys, _Petromyzon marinus unicolor_, the variety land-locked in the lakes of Central New York, metamorphose and assume the form of the adult. They are now about six or eight inches long. The externally segmented condition of the body disappears. The eyes appear to grow out through the skin and become plainly visible and functional. The mouth is no longer filled with vertical membranous sheets to act as a sieve, but it contains nearly one hundred and fifty sharp and chitinous teeth, arranged in rows that are more or less concentric and at the same time presenting the appearance of circular radiation. These teeth are very strong, with sharp points, and in structure each has the appearance of a hollow cone of chitin placed over another cone or papilla. A little below the center of the mouth is the oral opening, which is circular and contains a flattened tongue which bears finer teeth of chitin set closely together and arranged in two interrupted (appearing as four) curved rows extending up and down from the ventral toward the dorsal side of the mouth. Around the mouth is a circle of soft membrane finally surrounded by a margin of fimbriæ or small fringe. This completes the apparatus with which the lamprey attaches itself to its victims, takes its food, carries stones, builds and tears down its nest, seizes its mate, holds itself in position in a strong current, and climbs over falls."

=Mischief Done by Lampreys.=--"The most common economic feature in the entire life history of these animals is their feeding habits in this (spawning) stage, their food now consisting wholly of the blood (and flesh) of fishes. A lamprey is able to strike its suctorial mouth against a fish, and in an instant becomes so firmly attached that it is very rarely indeed that the efforts of the fish will avail to rid itself of its persecutor. When a lamprey attaches itself to a person's hand in the aquarium, it can only be freed by lifting it from the water. As a rule it will drop the instant it is exposed to the open air, although often it will remain attached for some time even in the open air, or may attach itself to an object while out of water.

"Nearly all lampreys that are attached to fish when they are caught in nets will escape through the meshes of the nets, but some are occasionally brought ashore and may hang on to their victim with bulldog pertinacity.

"The fishes that are mostly attacked are of the soft-rayed species, having cycloid scales, the spiny-rayed species with ctenoid scales being most nearly immune from their attacks. We think there may be three reasons for this: 1st, the fishes of the latter group are generally more alert and more active than those of the former, and may be able more readily to dart away from such enemies; 2d, their scales are thicker and stronger and appear to be more firmly imbedded in the skin, consequently it is more difficult for the lampreys to hold on and cut through the heavier coat-of-mail to obtain the blood of the victim; 3d, since the fishes of the second group are wholly carnivorous and in fact almost exclusively fish-eating when adult, in every body of water they are more rare than those of the first group, which are more nearly omnivorous. According to the laws and requirements of nature the fishes of the first group must be more abundant, as they become the food for those of the second, and it is on account of their greater abundance that the lampreys' attacks on them are more observed.

"There is no doubt that the bullhead, or horned pout (_Ameiurus nebulosus_), is by far the greatest sufferer from lamprey attacks in Cayuga Lake. This may be due in part to the sluggish habits of the fish, which render it an easy victim, but it is more likely due to the fact that this fish has no scales and the lamprey has nothing to do but to pierce the thick skin and find its feast of blood ready for it. There is no doubt of the excellency of the bullhead as a food-fish and of its increasing favor with mankind. It is at present the most important food- and market-fish of the State (New York), being caught by bushels in the early part of June when preparing to spawn. As we have observed at times more than ninety per cent. of the catch attacked by lampreys, it can readily be seen how very serious are the attacks of this terrible parasite which is surely devastating our lakes and streams."

=Migration or "Running" of Lampreys.=--"After thus feeding to an unusual extent, their reproductive elements (gonads) become mature and their alimentary canals commence to atrophy. This duct finally becomes so occluded that from formerly being large enough to admit a lead-pencil of average size when forced through it, later not even liquids can pass through, and it becomes nearly a thread closely surrounded by the crowding reproductive organs. When these changes commence to ensue, the lampreys turn their heads against the current and set out on their long journeys to the sites that are favorable for spawning, which here may be from two to eight miles from the lake. In this migration they are true to their instincts and habits of laziness in being carried about, as they make use of any available object, such as a fish, boat, etc., that is going in their direction, fastening to it with their suctorial mouths and being borne along at their ease. During this season it is not infrequent that as the Cornell crews come in from practice and lift their shells from the water, they find lampreys clinging to the bottoms of the boats, sometimes as many as fifty at one time. They are likely to crowd up all streams flowing into the lake, inspecting the bed of the stream as they go. They do not stop until they reach favorable spawning sites, and if they find unsurmountable obstacles in their way, such as vertical falls or dams, they turn around and go down-stream until they find another, up which they go. This is proved every spring by the number of adult lampreys which are seen temporarily in Pall Creek and Cascadilla Creek. In each of these streams, about a mile from its mouth, there is a vertical fall over thirty feet in height which the lampreys cannot surmount, and in fact they have never been seen attempting to do so. After clinging with their mouths to the stones at the foot of the falls for a few days, they work their way down-stream, carefully inspecting all the bottom for suitable spawning sites. They do not spawn in these streams because there are too many rocks and no sand, but finally enter the only stream (the Cayuga Lake inlet) in which they find suitable and accessible spawning sites.

"The three-toothed lampreys (_Entosphenus tridentatus_) of the West Coast climb low falls or rapids by a series of leaps, holding with their mouths to rest, then jumping and striking again and holding, thus leap by leap gaining the entire distance.

"The lampreys here have never been known to show any tendency or ability to climb, probably because there are no rapids or mere low falls in the streams up which they would run. In fact, as the inlet is the only stream entering Cayuga Lake in this region which presents suitable spawning conditions and no obstructions, it can be seen at once that all the lampreys must spawn in this stream and its tributaries.

"In 'running' they move almost entirely at night, and if they do not reach a suitable spawning site by daylight, they will cling to roots or stones during the day and complete their journey the next night. This has been proven by the positive observation of individuals. Of the specimens that run up early in the season, about four-fifths are males. Thus the males do not exactly precede the females, because we have found the latter sex represented in the stream as early in the season as the former, but in the earlier part of the season the number of the males certainly greatly predominates. This proportion of males gradually decreases, until in the middle of the spawning season the sexes are about equally represented, and toward the latter part of the season the females continue to come until they in turn show the greater numbers. Thus it appears very evident in general that the reproductive instinct impels the most of the males to seek the spawning ground before the most of the females do. However, it should be said that neither the males nor the females show all of the entirely sexually mature features when they first run up-stream in the beginning of the season, but later they are perfectly mature and 'ripe' in every regard when they first appear in the stream. When they migrate, they stop at the site that seems to suit their fancy, many stopping near the lake, others pushing on four or five miles farther up-stream. We have noted, however, that later in the season the lower courses become more crowded, showing that the late comers do not attempt to push up-stream as far as those that came earlier. Also it thus follows, from what was just said about late-running females, that in the latter part of the season the lower spawning beds are especially crowded with females. In fact, during the early part of the month of June we have found, not more than half a mile above the lowest spawning bed, as many as five females on a spawning nest with but one male; and in that immediate vicinity many nests indeed were found at that time with two or three females and but one male.

"Having arrived at a shoal which seems to present suitable conditions for a spawning nest, the individual or pair commences at once to move stones with its mouth from the centre to the margin of an area one or two feet in diameter. When many stones are thus placed, especially at the upper edge, and they are cleaned quite free of sediment and algæ, both by being moved and by being fanned with the tail, and when the proper condition of sand is found in the bottom of the basin thus formed, it is ready to be used as a spawning bed or nest. A great many nests are commenced and deserted. This has been left as a mystery in publications on the subject, but we are well convinced that it is because the lampreys do not find the requisites or proper conditions of bottom (rocks, sand, etc., as given below) to supply all their needs and fulfill all conditions for ideal sites. This desertion of half-constructed nests is just what would be expected and anticipated in connection with the explanation of 'Requisite Conditions for Spawning,' given below, because some shallows contain more sand and fewer stones, and others contain many larger stones but no sand, while others contain pebbles lying over either rocks or sand. The lampreys remove some of the material, and if they do not find all the essentials for a spawning nest, the site is deserted and the creatures move on."

=Requisite Conditions for Spawning with Lampreys.=--"For a spawning site two conditions are immediately essential--proper conditions of water and suitable stream bed or bottom. Of course with these it is essential that no impassable barriers (dam or falls) exist between the lake and the spawning sites to prevent migration at the proper 'running' season. Lampreys will not spawn where there is no sand lying on the bottom between the rocks, as sand is essential in covering the eggs (see remarks on the 'Spawning Process'); neither will they spawn where the bottom is all sand and small gravel, as they cannot take hold of this material with their mouths to construct nests or to hold themselves in the current, and they would not find here pebbles and stones to carry over the nest while spawning, as described elsewhere. It can thus be seen that, as suggested above, the reason they do not spawn in Fall Creek and Cascadilla Creek, between the lake and the falls, is that the beds of these streams are very rocky, being covered only with large stones and no sand. There is no doubt that the lampreys find here suitable conditions of water, but they do not remain to spawn on account of the absence of the proper conditions of stream bed. Again, they do not spawn in the lower course of the inlet for a distance of nearly two miles from the lake, because near the lake the bed of the stream is composed of silt, while for some distance above this (up-stream) there is nothing but sand. Farther up-stream are found pebbles and stones commingled with sand, which combination satisfies the demands of the lampreys for material in constructing nests and covering eggs. The accessibility of these sites, together with their suitable conditions, render the inlet the great and perhaps the only spawning stream of the lake; and, doubtless, all the mature lampreys come here to spawn, excepting a few which spawn in the lower part of Six-mile Creek, a tributary of the inlet.

"As the course of the stream where the beds abound is divided into pools, separated by stony ripples or shallows, the nests must be made at the ends of the pools. Of the spawning beds personally observed during several seasons, nine-tenths of the entire number were formed just above the shallows at the lower ends of the pools, while only a few were placed below them. An advantage in forming the nest above the shoals rather than below it is that in the former place the water runs more swiftly over the lower and middle parts of such a bed than at its upper margin, since the velocity decreases in either direction from the steeper part of the shallows; and any organic material or sediment that would wash over the upper edge of the nest is thus carried on rather than left as a deposit. When formed below the shallows, owing to the decreased velocity at the lower part of the nest compared with that at the upper, the sediment is likely to settle in the hollow of the nest, and, through the process of decay of the organic material, prove disastrous or unfavorable for the developing embryos.

"The necessity of sand in the spawning bed indicates the explanation of why we see so many shallows which have no spawning lampreys upon them, while there are others in the same vicinity that are crowded. There will be no nests formed if there is too little or too much sand, not enough or too many stones, or stones that are all too small or all too large. The stones must vary from the size of an egg to the size of a man's hand, and must be intermingled with sand without mud or rubbish.

"The lampreys choose to make their spawning nests just where the water flows so swiftly that it will carry the sand a short distance, but will not sweep it out of the nest. This condition furnishes not only force to wash the sand over the eggs when laid, but also keeps the adult lampreys supplied with an abundance of fresh water containing the dissolved air needed for their very rapid respiration. Of course in such rapid water the eggs are likely to be carried away down-stream, but Nature provides against this by the fact that they are adhesive, and the mating lampreys stir up the sand with their tails, thus weighing down the freshly laid eggs and holding them in the nest. Hence the necessity of an abundance of sand at the spawning site."

=The Spawning Process with Lampreys.=--"There is much interest in the study of the spawning process, as it is for the maintenance of the race that the lampreys risk and end their lives; and as they are by far the lowest form of vertebrates found within the United States, a consideration of their actions and apparent evidences of instinct becomes of unusual attraction. Let us consider one of those numerous examples in which the male migrates before the female. When he comes to that portion of the stream where the conditions named above are favorable, he commences to form a nest by moving and clearing stones and making a basin with a sandy bottom about the size of a common wash-bowl. Several nests may be started and deserted before perfect conditions are found for the completion of one. The male may be joined by a female either before or after the nest is completed. There is at once harmony in the family; but if another male should attempt to intrude, either before or after the coming of the female, he is likely to be summarily dealt with and dismissed at once by the first tenant. As soon as the female arrives she too commences to move pebbles and stones with her mouth.

"Sometimes the nest is made large enough to contain several pairs, or often unequal numbers of males and females; or they may be constructed so closely together as to form one continuous ditch across the stream, just above the shallows. Many stones are left at the sides and especially at the upper margin of the nest, and to these both lampreys often cling for a few minutes as though to rest. While the female is thus quiet, the male seizes her with his mouth at the back of her head, clinging as to a fish. He presses his body as tightly as possible against her side, and loops his tail over her near the vent and down against the opposite side of her body so tightly that the sand, accidentally coming between them, often wears the skin entirely off of either or both at the place of closest contact. In most observed instances the male pressed against the right side of the female, although there is no unvarying rule as to position. The pressure of the male thus aids to force the eggs from the body of the female, which flow very easily when ripe. The vents of the two lampreys are thus brought into close proximity, and the conspicuous genital papilla of the male serves to guide the milt directly to the issuing spawn. There appears to be no true intromission, although definite observation of this feature is quite difficult, and, in fact, impossible. During the time of actual pairing, which lasts but a few seconds, both members of the pair exhibit tremendous excitement, shaking their bodies in rapid vibrations and stirring up such a cloud of sand with their tails that their eggs are at once concealed and covered. As the eggs are adhesive and non-buoyant, the sand that is stirred up adheres to them immediately and covers most of them before the school of minnows in waiting just below the nest can dart through the water and regale themselves upon the eggs of these enemies of their race; but woe to the eggs that are not at once concealed. We would suggest that the function of the characteristic anal fin, which is possessed only by the female, and only at this time of year, may be to aid in this vastly important process of stirring up the sand as the eggs are expelled; and the explanation of the absence of such a fin from the ventral side of the tail of the male may be found in the fact that it could not be used for the same purpose at the instant when most needed, since the male is just then using his tail as a clasping organ to give him an essential position in pairing. As soon as they shake together they commence to move stones from one part of the nest to another, to bring more loose sand down over their eggs. They work at this from one to five minutes, then shake again, thus making the intervals between mating from one to five minutes, with a general average of about three and a half minutes.

"Although their work of moving stones does not appear to be systematic in reference to the placing of the pebbles, or as viewed from the standpoint of man, it does not need to be so in order to perfectly fulfill all the purposes of the lampreys. As shown above in the remarks on the spawning habits of the brook lampreys, the important end which they thus accomplish is the loosening and shifting of the sand to cover their eggs; and the more the stones are moved, even in the apparently indiscriminate manner shown, the better is this purpose achieved. Yet, in general, they ultimately accomplish the feat of moving to the lower side of the nest all the stones they have placed or left at the upper margin. At the close of the spawning season when the nest is seen with no large pebbles at its upper margin, but quite a pile of stones below, it can be known that the former occupants completed their spawning process there; but if many small stones are left at the upper edge and at the sides, and a large pile is not formed at the lower edge, it can be known that the nest was forsaken or the lampreys removed before the spawning process was completed. The stones they move are often twice as heavy as themselves, and are sometimes even three or four times as heavy. Since they are not attempting to build a stone wall of heavy material, there is no occasion for their joining forces to remove stones of extraordinary size, and they rarely do so, although once during the past spring (1900) we saw two lake lampreys carrying the same large stone down-stream across their nest. Although this place was occupied by scores of brook lampreys, there were but three pairs of lake lampreys seen here. It is true that one of these creatures often moves the same stone several times, and many even attempt many times to move a stone that has already been found too heavy for it; but sooner or later the rock may become undermined so that the water will aid them, and they have no way of knowing what they can do under such circumstances until they try. Also, the repeated moving of one stone may subserve the same purpose for the lamprey in covering its eggs with sand as would the less frequent removal of many.

"When disturbed on the spawning nest, either of the pair will return to the same nest if its mate is to be found there; but if its mate is in another place, it will go to it, and if its mate is removed or killed, it is likely to go to any part of the stream to another nest. When disturbed, they often start up-stream for a short distance, but soon dart down-stream with a velocity that is almost incredible. They can swim faster than the true fishes, and after they get a start are generally pretty sure to make good their escape, although we have seen them dart so wildly and frantically down-stream that they would shoot clear out on the bank and become an easy victim of the collector. This peculiar kind of circumstance is most likely to happen with those lampreys that are becoming blinded from long exposure to the bright light over the clear running water. If there is a solitary individual on a nest when disturbed, it may not return to that nest, but to any that has been started, or it may stay in the deep pool below the shallows until evening and then move some distance up-stream. When the nest is large and occupied by several individuals, those that are disturbed may return to any other such nest. We have never seen evidence of one female driving another female out of a spawning-nest; and from the great number of nests in which we have found the numbers of the females exceeding those of the males, we would be led to infer that the former live together in greater harmony than do the males.

"Under the subject of the number of eggs laid, we should have said that at one shake the female spawns from twenty to forty. We once caught in fine gauze twenty-eight eggs from a female at one spawning instant. In accordance with the frequency of spawning stated, and the number of eggs contained in the body of one female, the entire length of time given to the spawning process would be from two to four days. This agrees with the observed facts, although the lampreys spend much time in moving stones and thoroughly covering the nests with sand. Even after the work of spawning and moving stones is entirely completed, they remain clinging to rocks in various parts of the stream, until they are weakened by fungus and general debility, when they gradually drift down-stream.

"In forming nests there is a distinct tendency to utilize those sites that are concealed by overhanging bushes, branches, fallen tree-tops, or grass or weeds, probably not only for concealment, but also to avoid the bright sunlight, which sooner or later causes them to go blind, as it does many fishes when they have to live in water without shade. Toward the end of the spawning season, it is very common to see blind lampreys clinging helplessly to any rocks on the bottom, quite unable to again find spawning-beds. However, at such times they are generally spent and merely awaiting the inevitable end.

"As with the brook lamprey, the time of spawning and duration of the nesting period depend upon the temperature of the water, as does also the duration of the period of hatching or development of the embryo. They first run up-stream when the water reaches a temperature of 45° or 48° Fahr., and commence spawning at about 50°. A temperature of 60° finds the spawning process in its height, and at 70° it is fairly completed. It is thus that the rapidity with which the water becomes heated generally determines the length of time the lampreys remain in the stream. This may continue later in the season for those that run later, but usually it is about a month or six weeks from the time the first of this species is seen on a spawning-nest until the last is gone."

=What becomes of Lampreys after Spawning?=--"There has been much conjecture as to the final end of the lampreys, some writers contending that they die after spawning, others that they return to deep water and recuperate, and yet others compromise these two widely divergent views by saying that some die and others do not. The fact is that the spawning process completely wears out the lampreys, and leaves them in a physical condition from which they could never recover. They become stone-blind; the alimentary canal suffers complete atrophy; their flesh becomes very green from the katabolic products, which find the natural outlet occluded; they lose their rich yellow color and plump, symmetrical appearance; their skin becomes torn, scratched, and worn off in many places, so that they are covered with sores, and they become covered with a parasitic or sarcophytic fungus, which forms a dense mat over almost their entire bodies, and they are so completely debilitated and worn out that recovery is entirely out of the question. What is more, the most careful microscopical examination of ovaries and testes has failed to reveal any evidence of new gonads or reproductive bodies. This is proof that reproduction could not again ensue without a practical rebuilding of the animals, even though they should regain their vitality. A. Mueller, in 1865, showed that all the ova in the lamprey were of the same size, and that after spawning no small reproductive bodies remained to be developed later. This is strong evidence of death after once spawning.

"One author writes that an argument against the theory of their dying after spawning can be found in the fact that so few dead ones have been found by him. However, many can be found dead if the investigator only knows how and where to look for them. We should not anticipate finding them in water that is shallow enough for the bottom to be plainly seen, as there the current is strong enough to move them. It is in the deep, quiet, pools where sediment is depositing that the dead lampreys are dropped by the running water, and there they sink into the soft ooze.

"The absence of great numbers of dead lampreys from visible portions of the stream cannot be regarded as important evidence against the argument that they die soon after spawning once, as the bodies are very soon disintegrated in the water. In the weir that we maintained in 1898, a number of old, worn-out, and fungus-covered lampreys were caught drifting down-stream; some were dead, some alive, and others dying and already insensible, but none were seen going down that appeared to be in condition to possibly regain their strength."