their kind, they move by the alternate dilatation and contraction of
the disk, but in the Zygodactyla these undulations have a certain
graceful indolence, very unlike the more rapid movements of many of
the Medusæ. It often remains quite motionless for a long time, and
then, if you try to excite it by disturbing the water in the tank, or
by touching it, it heaves a slow, lazy sigh, with the whole body
rising slightly as it does so, and then relapses into its former
inactivity. Indeed, one cannot help being reminded, when watching the
variety in the motions of the different kinds of Jelly-fishes, of the
difference of temperament in human beings. There are the alert and
active ones, ever on the watch, ready to seize the opportunity as it
comes, but missing it sometimes from too great impatience; and the
slow, steady people, with very regular movements, not so quick
perhaps, but as successful in the long run; and the dreamy, indolent
characters, of which the Zygodactyla is one, always floating languidly
about, and rarely surprised into any sudden or abrupt expression. One
would say, too, that they have their aristocratic circles; for there
is a delicate, high-bred grace about some of them quite wanting in the
coarser kinds. The lithe, flexible form of the greyhound is not in
stronger contrast to the heavy, square build of the bull dog, than are
some of the lighter, more frail species of Jelly-fish to the more
solid and clumsy ones. Among these finer kinds we would place the
Tima. (Fig. 76.)
_Tima_. (_Tima formosa_ AG.)
One's vocabulary is soon exhausted in describing the different degrees
of consistency in the substance of Jelly-fishes. Delicate and
transparent as is the Tima, it has yet a certain robustness and
solidity beside the Oceania, described above. In fact, all are
gelatinous, all are more or less transparent, and it is not easy to
describe the various shades of solidity in jelly. Perhaps they may be
more accurately represented by the impression made upon the touch than
upon the sight. If, for instance, you place your hand upon a
Zygodactyla, you feel that you have come in contact with a substance
that has a positive consistency; but if you dip your finger into a
bowl where a Tima is swimming, and touch its disk, you will feel no
difference between it and the water in which it floats, and will not
be aware that you have reached it till the animal shrinks away from
the contact.
[Illustration: Fig. 76. Tima; half natural size.]
[Illustration: Fig. 77. One of the lips of the mouth at the
extremity of the long proboscis; _m_ mouth, _d_ digestive cavity,
_c_ chymiferous tube.]
The adult Tima, represented in Fig. 76, is not more than an inch and a
half or two inches in diameter. Instead of countless tubes diverging
from the digestive cavity to the margin of the disk, as in the
Zygodactyla, there are but four. The digestive cavity in the Tima is
much smaller than in the Zygodactyla, and is placed at the end of the
proboscis, which is long, and hangs down far below the disk. This
removal of the digestive cavity to the extremity of the proboscis
gives to the tubes arising from it a very different and much sharper
curve than they have in the Zygodactyla. In the Tima they start from
the end of the proboscis, as may be seen in the wood-cut (Fig. 76),
and then turn abruptly off, when they arrive at the under surface of
the disk, to reach its margin. The disk has, as usual, its veil and
its fringe of tentacles; the tentacles in the full-grown Tima are
few,--seven in all the four intermediate spaces between the tubes,
with one at the base of each tube, making thirty-two in all. The
ovaries, which are milk-white, follow the line of the tubes, as in the
Zygodactyla, and have very undulating folds when full of eggs. The
tubes meet in the digestive cavity, the margin of which spreads out to
form four ruffled edges that hang down from it. One of these ruffles,
considerably magnified, is represented in Fig. 77. In Fig. 78 we have
a portion of the Hydroid stock from which this Jelly-fish arises, also
greatly magnified. The Tima is very active, yet not abrupt in its
motions; but when in good condition it is constantly moving about,
rising to the surface by the regular pulsations of the disk, or
swimming from side to side, or poising itself quietly in the water,
giving now and then a gentle undulation to keep itself in position.
[Illustration: Fig. 78. Magnified head of Hydrarium of Tima.]
Though not a very frequent visitor of our shores, the appearance of
the Tima is not limited by the seasons, since they are found at all
times of the year. It is a fact, unexplained as yet, that the Tima and
many other Jelly-fishes are never seen except when full grown. What
may be the haunts and habits of these animals from the time of their
hatching till they make their appearance again in the adult condition,
is not known, though it is probable that they remain at the bottom
during this period, and only come to the surface to spawn. This
impression is confirmed by the observations made upon a very young
Cyanea which was kept for a long time in confinement; but a question
of this kind cannot of course be settled by a single experiment.[6]
[Footnote 6: Since the above was written, I have had an opportunity of
learning some additional facts respecting the habits of the young
Cyanea, which may, perhaps, apply to other Jelly-fishes also. Having
occasion to visit the wharves at Provincetown at about four o'clock
one morning, I was surprised to find thousands of the spring brood of
Cyaneæ, hitherto supposed to pass the early period of their existence
wholly in deep water, floating about near the surface. They varied in
size, some being no larger than a three-cent-piece, while others were
from an inch in diameter to three inches. It would seem that they make
their appearance only during the earliest morning hours, for at seven
o'clock, when I returned to the same spot, they had all vanished. It
may be that other young Medusæ have the same habits of early rising,
and that instead of coming to bask in the midday sunshine, like their
elders, they prefer the cooler hours of the dawn. (_A. Agassiz_.)]
_Melicertum_. (_Melicertum campanula_ PÉR. et LES.)
A pretty Medusa, smaller and far more readily obtained than the Tima,
is the Melicertum. (Fig. 80.) Its disk has a yellowish hue, and from
its margin hangs a heavy row of yellow tentacles, while the eight
ovaries (Fig. 79) are of a darker shade of the same color. This little
golden-tinted Jelly-fish, moving through the water with short, quick
throbs, produced by the rapid rise and fall of the disk, is a very
graceful object. Its bright color, made particularly prominent by the
darker undulating lines of the ovaries, which become very marked near
the spawning season, renders it more conspicuous in the water than one
would suppose from its size; for it does not measure more than an inch
in height when full grown. (See Fig. 80.)
[Illustration: Fig. 79. Melicertum campanula seen from above; _m_
mouth, _o o_ ovaries, _t t_ tentacles. (_Agassiz_.)]
_Development of Melicertum and Tima_.
[Illustration: Fig. 80. Melicertum seen in profile; natural size.]
In the Melicertum and Tima we have had the good fortune to trace the
process by which the eggs are changed into Hydroid communities. If any
one has a curiosity to follow for themselves this singular history of
alternate generations, the Melicertum is a good subject for the
experiment, as it thrives well in confinement. After keeping a number
of them in a large glass jar for a couple of days at the time of
spawning, it will be found that the ovaries, which were at first quite
full of eggs, are emptied, and that a number of planulæ; are swimming
about near the bottom of the vessel. After a day or two the outline of
these planulæ, spherical at first, becomes pear-shaped (see Fig. 81),
and presently they attach themselves by the blunt end to the bottom of
the jar. (Fig. 82.) Thus their Hydroid life begins; they elongate
gradually, the horny sheath is formed around them, tentacles arise on
the upper end, short and stunted at first, but tapering rapidly out
into fine flexible feelers, the stem branches, and we have a little
Hydroid community (Fig. 83), upon which, in the course of the
following spring, the reproductive calycles containing the Medusæ buds
will be developed, as in the case of the Eucope and Clytia. The Tima
passes through exactly the same process, though the shape of the
planulæ and the appearance of the young differ from that of the
Melicertum, as may be seen in Fig. 78, where a single head of the Tima
Hydroid, greatly magnified, is represented. By combining the above
observations upon the development of the Hydroids of the Melicertum
and Tima with those previously mentioned upon the young Medusa arising
from reproductive calycles in the Eucope and Clytia, we get a complete
picture of all the changes through which any one of these Hydroid
Medusæ passes, from its Hydroid condition to the moment when it enters
upon an independent existence as a free Jelly-fish.
[Illustration: Fig. 81. Planula of Melicertum; magnified.]
[Illustration: Fig. 82. Cluster of planulæ just attached to the
ground.]
[Illustration: Fig. 83. Young Hydrarium developed from planulæ;
magnified.]
(_Laomedea amphora_ AG.)
The Medusæ of the Campanularians are not all free. On the contrary, in
many of the species they always remain attached to the Hydroid, never
attaining so high a development as the free Medusæ, and withering on
the stem after having laid their eggs. Such is the _Laomedea amphora_,
quite common on all the bridges connecting Boston with the country,
where, on account of the large amount of food brought down from the
sewers by the river, they thrive wonderfully, growing to a great size,
sometimes measuring from a foot to eighteen inches in height.
_Sertularians_.
[Illustration: Fig. 84. Colony of Dynamena pumila; natural size.]
[Illustration: Fig. 85. Magnified portion of Fig. 84.]
The Sertularians form another group of Hydroids closely allied to the
Campanularians, though differing from them in the arrangement of the
sterile Hydræ upon the stem. Among these one of the most numerous is
the Dynamena (_Dynamena pumila_ Lamx., Fig. 84), which hangs its
yellowish fringes from almost every sea-weed above low-water-mark. It
is especially thick and luxuriant on the fronds of our common _Fucus
vesiculosus_. The color is usually of a pale yellow, though sometimes
it is nearly white, and when first taken from the water it has a
glittering look, such as a white frost leaves on a spray of grass.
Fig. 84 represents such a cluster in natural size, while Fig. 85 shows
a piece of the stem highly magnified, with a reproductive calycle
attached to the side of a sterile Hydra stem. Many of these
Sertularian Hydroids assume the most graceful forms, hanging like long
pendent streamers from the Laminaria, or in other instances resembling
miniature trees. One of these tree-like Sertularians (_Dyphasia
rosacea_ Ag.), abundant on all rocks in sheltered places immediately
below low-water-mark, is represented in Fig. 86. In both these
Sertularians the Medusæ wither on the stock, never becoming free. The
free Medusæ of the Sertularians are only known in their adult
condition in a single genus, which is closely allied to Melicertum,
and which is produced from a Hydroid genus called Lafoea. Fig. 87
represents one of these young Sertularian Medusæ (_Lafoea cornuta_
Lamx.).
[Illustration: Fig. 86. Dyphasia rosacea, natural size.]
[Illustration: Fig. 87. Medusa of Lafoea.]
_Tubularians_.
In the Sertularian and Campanularian Hydroids we have found that the
communities consist generally of a large number of small individuals,
so small, indeed, that it is hardly possible at first glance to
distinguish the separate members of these miniature societies. Among
the Tubularians, on the contrary, the communities are usually composed
of a small number of comparatively large individuals; and indeed these
Hydroids may even grow singly, as in the case of the Hybocodon (Fig.
104), which attains several inches in height. There is also another
general feature in which the Tubularians differ from both the other
groups of Hydroids. In the latter, the horny sheath which encloses the
stem extends to form a protecting calycle around the Hydra heads. This
protecting calycle is wanting round the heads of the Tubularians,
though their stems are surrounded by a sheath.
_Sarsia_. (_Coryne mirabilis_ AG.)
[Illustration: Fig. 88. Colony of Coryne; natural size.
(_Agassiz_.)]
[Illustration: Fig. 89. Magnified head of Coryne; _a_ stem, _t_
tentacles, _o_ mouth, _v_ body, _d_ Medusa. (Agassiz.)]
[Illustration: Fig. 90. Free Medusa of Coryne. (_Agassiz_.)]
Among the most common of our Tubularians is a small, mossy Hydroid
(Fig. 88), covering the rocks between tides, in patches of several
feet in diameter. Fig. 89 represents a single head from this little
mossy tuft greatly magnified, in which is seen the medusa bud arising
from the stem by the process already described in the other Hydroids.
In Fig. 90 we have the little Jelly-fish in its adult condition, about
the size of a small walnut, with a wide circular opening, through
which passes the long proboscis, hanging from the under surface of the
disk to a considerable distance below its margin. The four tentacles
are of an immense length when compared to the size of the animal. As a
general thing, the tentacles are less numerous in the Tubularian
Medusæ than in those arising from other Hydroids; they want also the
singular limestone concretions found at the base of the tentacles in
the Campanularian Medusæ. In Fig. 91 we have one of the Tubularian
Medusæ (_Turris vesicaria_ A. Ag.) which lifts a rather larger number
of tentacles than is usual among these Jelly-fishes. We never find the
tentacles multiplying almost indefinitely in them, as in Zygodactyla
and Eucope. The little Jelly-fish described above is known as Sarsia,
while its Hydroid is called Coryne. These names having been given to
the separate phases of its existence before their connection was
understood, and when they were supposed to represent two distinct
animals. They are especially interesting with reference to the history
of Hydroids in general, because they were among the first of these
animals in whom the true relation between the different phases of
their existence was discovered. Lesson named the Sarsia after the
great Norwegian naturalist, Sars, to whom we owe so large a part of
what is at present known respecting this curious subject of alternate
generations.
[Illustration: Fig. 91. Turris vesicaria; natural size.]
_Bougainvillia_. (_Bougainvillia superciliaris_ AG.)
The Bougainvillia (Fig. 92), is one of our most common Jelly-fishes,
frequenting our wharves as well as our sea-shore during the spring. The
tentacles are arranged in four bunches or clusters at the junction of
the radiating tubes with the circular tube, from which they may be seen
extending in every direction whenever these animals remain quietly
suspended in the water,--a favorite attitude with them, and one which
they retain sometimes for days, seeming to make no effort beyond that of
gently playing their tentacles to and fro (Fig. 92). These tentacles are
capable of immense extension, sometimes to ten or fifteen times the
diameter of the bell. The proboscis is not simple as in the Sarsia, but
looks like a yellow urn suspended at its four corners from the
chymiferous tubes. The oral opening is entirely concealed by clusters of
shorter tentacles surrounding the mouth in a close wreath, on which the
eggs are supported. A highly magnified branch of the Hydroid stock from
which this Medusa arises is represented in Fig. 93. There we see the
little Jelly-fishes in different degrees of development on the stem,
while in Figs. 94-97 they are given separately and still more enlarged.
In Fig. 94 the outline of the Jelly-fish is still oval, the proboscis is
but just formed, and the tentacles appear only as round swellings or
knobs. In Fig. 95 a depression has taken place at the upper end,
presently to be an opening, the proboscis is enlarged, and the tentacles
lengthened, but still turned inward. In Fig. 96 the appendages of the
proboscis are quite conspicuous, the tentacles are turned outward, and
the Jelly-fish is almost ready to break from its attachment, having
assumed its ultimate outline. Fig. 97 represents it just after it has
separated from the stem, when it has only two tentacles at each cluster
and simple knobs around the mouth, instead of the complicated branching
tentacles of the adult.
[Illustration: Fig. 92. Bougainvillia; magnified.]
[Illustration: Fig. 93. Hydrarium of Bougainvillia; magnified.]
[Illustration: Figs. 94, 95, 96. Medusæ buds of Fig. 93, in
different degrees of development.]
[Illustration: Fig. 97. Young Medusa just freed from the Hydroid;
magnified.]
_Tubularia_. (_Tubularia Couthouyi_ AG.)
There are several other Tubularians common in our waters which should
not be passed over without mention, although as this little book is by
no means intended as a complete text-book, but rather as a volume of
hints for amateur collectors, we would avoid as much as possible
encumbering it with many names, or with descriptions already given in
more comprehensive works. This Tubularia is interesting, however, from
the fact that the Medusæ buds are never freed from the stem, and do
not develop into full-grown Jelly-fishes, but always remain abortive.
Fig. 98 represents one head of such a Hydroid with the Medusæ buds
pendent from it in a thick cluster, while in Fig. 99 we have a few of
them sufficiently magnified to show that, though presenting the four
chymiferous tubes, they are otherwise exceedingly simple in structure,
as compared with the free Jelly-fishes.
[Illustration: Fig. 98. Tubularia; magnified. (_Agassiz_.)]
[Illustration: Fig. 99. Part of cluster of Medusæ of Fig. 98;
magnified. (_Agassiz_.)]
_Hydractinia_. (_Hydractinia polyclina_ AG.)
This is another Tubularian, covering the surface of rocks in
tide-pools, or attaching itself upon shells inhabited by hermit crabs.
Indeed it was upon these shells that the Hydractinia was first
noticed, and it was long supposed that the wanderings to which the
little colony was thus subjected were necessary for its healthy
development. But subsequent observations have shown that it attaches
itself quite as frequently to the solid rock as to these nomadic
shells. It has a rosy color, and, being very small, it looks, until
one examines it closely, more like a thick red carpet of soft moss,
than like a colony of animals. These communities are distinct in sex,
the fertile individuals in each being either all male or all female.
In Fig. 100 we have a portion of a female colony, representing one
fertile head, in which the buds are crowded with Medusæ; one sterile
head, surrounded by its wreath of tentacles; and still another member
of the society whose office is not fully understood, unless it be that
of a kind of purveyor, catching food for the rest. Fig. 101 represents
the corresponding individuals taken from a male colony. The sex makes
little difference in the appearance of the reproductive heads. All the
individuals of a Hydractinia colony are connected at the base by a
horny network, rising occasionally into points of a conical or
cylindrical shape. This polymorphism among the Tubularians is another
evidence of the relation between the Siphonophoræ, or floating
Hydroids, and the fixed Hydroids.
[Illustration: Fig. 100. Female colony of Hydractinia; _a_ sterile
individual, _b_ fertile individual producing female Medusæ, _c_
fertile individual with globular tentacles without Medusæ, _d_ _e_
_f_ _g_ _h_ _i_ Medusæ in different stages of growth, _o_ mouth
tentacles. (_Agassiz_.)]
[Illustration: Fig. 101. Male colony; _a_ _a_ sterile individuals,
_b_ fertile individuals producing male Medusæ, _d_; _o_ globular
tentacles, _t_ slender tentacles of sterile individual.
(_Agassiz_.)]
_Hybocodon_. (_Hybocodon prolifer_ AG.)
Among our Medusæ derived from a Tubularian stock is the Hybocodon,
viz. the hunchbacked Medusa (Fig. 102), a singular little Jelly-fish,
odd and unsymmetrical in shape, as its name indicates, and interesting
from its relations to one of our floating communities, the Nanomia,
presently to be described. Instead of the evenly proportioned bell of
the ordinary Medusæ, the Hybocodon has a one-sided outline (Fig. 102),
one large tentacle only being fully developed, while the others remain
always abortive, so that the whole weight of the structure is thrown
on one half of the bell. Upon this large tentacle small Jelly-fishes,
similar to the original, are produced by budding, this process going
on till ten or twelve such Jelly-fishes (Fig. 103) may be seen
suspended from the tentacle. Up to this time it has remained connected
with the Hydroid from which it arises, a rather large Tubularian,
usually growing singly (Fig. 104), and of a deep orange-red in color.
But at this stage of its existence it frees itself, and leads an
independent life hereafter, swimming about with a quick, darting
motion. In the account of the Nanomia, the homology between its scale,
or abortive Medusa, and the Hybocodon, is traced in detail, and I need
only allude to it here. Though this Medusa is so peculiar in
appearance, the Tubularian from which it is derived is very like the
_Tubularia Couthouyi_, already described. This is one of the instances
before alluded to, in which closely allied forms give rise to very
dissimilar ones, or, as in many cases, the very reverse of this takes
place, and closely allied forms arise from very dissimilar ones.
[Illustration: Fig. 102. Unsymmetrical free Medusa of Hybocodon;
_r_ _o_ chymiferous tubes, _v_ proboscis, _s_ circular tube, _m_
young Medusæ at base of long tentacle _t_. (_Agassiz_.)]
[Illustration: Fig. 103. Medusa bud of Hybocodon; _a_ base of
attachment, _o_ proboscis, _c_ circular tube, _d_ young Medusæ at
base of long tentacle _t_. (_Agassiz_.)]
[Illustration: Fig. 104. Single head of Hybocodon Hydroid; _a_
stem, _d_ Medusæ buds, _o_ tentacles round mouth. (_Agassiz_.)]
_Dysmorphosa_. (_Dysmorphosa fulgurans_ A. AG.)
Besides the budding at the base of the tentacle, as in Hybocodon, we
find another mode of development among Hydroid Medusæ, viz. that of
budding from the proboscis. One of our most common little
Jelly-fishes, the Dysmorphosa (Fig. 105), to which we owe the
occasional blue phosphorescence of the sea, so brilliant at times,
buds in this manner. Fig. 105 represents an adult Dysmorphosa, on the
proboscis of which may be seen three small buds in different stages of
development. In Fig. 106 the proboscis is more enlarged, showing one
of the little Jelly-fishes similar to the parent, just ready to drop
off. We need not wonder at the immense number of these animals, with
which the sea actually swarms at times, when we know that as fast as
they are dropped, and it takes but a few days to complete their
development, they each begin the same process; so that in the course
of a week or ten days one such Medusa, supposing it to have produced
six buds only, will have given rise to forty-two Jelly-fishes,
thirty-six of which may be equally prolific in the same short period.
These Medusæ budding thus, and swimming about, carrying their young
with them, bear such a close resemblance to the floating communities
of Hydroids formerly known as Siphonophoræ, that did we not know that
some of them arise from Tubularians, it would be natural to associate
them with the Siphonophoræ.
[Illustration: Fig. 105. Dysmorphosa seen in profile; magnified.]
[Illustration: Fig. 106. Magnified proboscis of Dysmorphosa with
young Medusæ budding from it.]
_Nanomia_. (_Nanomia cara_ A. AG.)