Seaside Studies in Natural History Part 5

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 ZyG.o.dactyla, 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.

[Ill.u.s.tration: Fig. 76. Tima; half natural size.]

[Ill.u.s.tration: 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 ZyG.o.dactyla, there are but four. The digestive cavity in the Tima is much smaller than in the ZyG.o.dactyla, 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 ZyG.o.dactyla. 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 s.p.a.ces 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 ZyG.o.dactyla, 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.

[Ill.u.s.tration: Fig. 78. Magnified head of Hydrarium of Tima.]

Though not a very frequent visitor of our sh.o.r.es, 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 sp.a.w.n. 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 Cyaneae, hitherto supposed to pa.s.s 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 Medusae 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. Aga.s.siz_.)]

_Melicertum_. (_Melicertum campanula_ PeR. 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 sp.a.w.ning 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.)

[Ill.u.s.tration: Fig. 79. Melicertum campanula seen from above; _m_ mouth, _o o_ ovaries, _t t_ tentacles. (_Aga.s.siz_.)]

_Development of Melicertum and Tima_.

[Ill.u.s.tration: 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 gla.s.s jar for a couple of days at the time of sp.a.w.ning, it will be found that the ovaries, which were at first quite full of eggs, are emptied, and that a number of planulae; are swimming about near the bottom of the vessel. After a day or two the outline of these planulae, 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 h.o.r.n.y 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 Medusae buds will be developed, as in the case of the Eucope and Clytia. The Tima pa.s.ses through exactly the same process, though the shape of the planulae 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 Medusae pa.s.ses, from its Hydroid condition to the moment when it enters upon an independent existence as a free Jelly-fish.

[Ill.u.s.tration: Fig. 81. Planula of Melicertum; magnified.]

[Ill.u.s.tration: Fig. 82. Cl.u.s.ter of planulae just attached to the ground.]

[Ill.u.s.tration: Fig. 83. Young Hydrarium developed from planulae; magnified.]

(_Laomedea amphora_ AG.)

The Medusae 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 Medusae, 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_.

[Ill.u.s.tration: Fig. 84. Colony of Dynamena pumila; natural size.]

[Ill.u.s.tration: 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 Hydrae 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 gra.s.s.

Fig. 84 represents such a cl.u.s.ter 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 a.s.sume 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 Medusae wither on the stock, never becoming free. The free Medusae 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 Medusae (_Lafoea cornuta_ Lamx.).

[Ill.u.s.tration: Fig. 86. Dyphasia rosacea, natural size.]

[Ill.u.s.tration: 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 h.o.r.n.y 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.)

[Ill.u.s.tration: Fig. 88. Colony of Coryne; natural size.

(_Aga.s.siz_.)]

[Ill.u.s.tration: Fig. 89. Magnified head of Coryne; _a_ stem, _t_ tentacles, _o_ mouth, _v_ body, _d_ Medusa. (Aga.s.siz.)]

[Ill.u.s.tration: Fig. 90. Free Medusa of Coryne. (_Aga.s.siz_.)]

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 pa.s.ses 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 Medusae than in those arising from other Hydroids; they want also the singular limestone concretions found at the base of the tentacles in the Campanularian Medusae. In Fig. 91 we have one of the Tubularian Medusae (_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 ZyG.o.dactyla 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.

[Ill.u.s.tration: 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-sh.o.r.e during the spring. The tentacles are arranged in four bunches or cl.u.s.ters 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 att.i.tude 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 cl.u.s.ters 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 k.n.o.bs. 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 a.s.sumed its ultimate outline. Fig. 97 represents it just after it has separated from the stem, when it has only two tentacles at each cl.u.s.ter and simple k.n.o.bs around the mouth, instead of the complicated branching tentacles of the adult.

[Ill.u.s.tration: Fig. 92. Bougainvillia; magnified.]

[Ill.u.s.tration: Fig. 93. Hydrarium of Bougainvillia; magnified.]

[Ill.u.s.tration: Figs. 94, 95, 96. Medusae buds of Fig. 93, in different degrees of development.]

[Ill.u.s.tration: 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 pa.s.sed 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 enc.u.mbering it with many names, or with descriptions already given in more comprehensive works. This Tubularia is interesting, however, from the fact that the Medusae 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 Medusae buds pendent from it in a thick cl.u.s.ter, 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.

[Ill.u.s.tration: Fig. 98. Tubularia; magnified. (_Aga.s.siz_.)]

[Ill.u.s.tration: Fig. 99. Part of cl.u.s.ter of Medusae of Fig. 98; magnified. (_Aga.s.siz_.)]

_Hydractinia_. (_Hydractinia polyclina_ AG.)