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.
[Illustration: FIG. 290.--_Polygnathus dubium_ Hinde. A Conodont from
the New York Devonian. (After Hinde.)]
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.
[Illustration: FIG. 291.--California Hagfish, _Polistotrema stouti_
Lockington.]
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.
[Illustration: FIG. 292.--Lamprey, _Petromyzon marinus_ L. Woods Hole,
Mass.]
=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):
[Illustration: FIG. 293.--_Petromyzon marinus unicolor_ (De Kay). Mouth
of Lake Lamprey, Cayuga Lake. (After Gage.)]
[Illustration: FIG. 294.--_Lampetra wilderi_ Jordan & Evermann. Larval
Brook Lamprey in its burrow in a glass filled with sand. (After Gage.)]
[Illustration: FIG. 295.--_Lampetra wilderi_ Jordan & Evermann. Mouth
of Brook Lamprey. Cayuga Lake. (After Gage.)]
"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.
[Illustration: FIG. 296.--Kamchatka Lamprey, _Lampetra camtschatica_
(Tilesius). Kamchatka.]
"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.
[Illustration: FIG. 297.--Oregon Lamprey, _Entosphenus tridentatus_,
ascending a brook. (Modified from a photograph by Dr. H. M. Smith.
Published by Prof. H. A. Surface.) Willamette River, Oregon.]
"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."
[Illustration: FIG. 297_a_.--Brook Lamprey, _Lampetra Wilderi_. (After
Gage.)]