Seaside Studies in Natural History Part 3

[Ill.u.s.tration: Fig. 38. Young Idyia seen from the a.n.a.l extremity, magnified; _a_ a.n.a.l opening, other letters as in Fig. 36.]

[Ill.u.s.tration: Fig. 39. Idyia somewhat older than Fig. 37, lettering as before; magnified.]

[Ill.u.s.tration: Fig. 40. Young Idyia in which the ambulacral tubes begin to ramify; magnified, letters as before.]

The Bolina, in its early condition, recalls the young Pleurobrachia.

At this period it has the same rapid motion, and when somewhat more advanced, long tentacles, resembling those of the Pleurobrachia, make their appearance (Fig. 41); it is only at a later period that the tentacles become contracted, while the large lobes (Fig. 42), so characteristic of Bolina, are formed by the elongation of the oral end of the body, the auricles becoming more conspicuous at the same time (Fig. 43). A little later the lobes enlarge, the movements become more lazy; it a.s.sumes both in form and habits the character of the adult Bolina.

[Ill.u.s.tration: Fig. 41. Young Bolina in stage resembling Pleurobrachia; greatly magnified.]

[Ill.u.s.tration: Fig. 42. Young Bolina seen from the broad side, with rudimentary auricles and lobes; magnified.]

[Ill.u.s.tration: Fig. 43. The same as Fig. 42, seen from the narrow side.]

The series of changes through which the Ctenophorae pa.s.s are as remarkable as any we shall have occasion to describe, though not accompanied with such absolutely different conditions of existence.

The comparison of the earlier stages of life in these animals with their adult condition is important, not only with reference to their mode of development, but also because it gives us some insight into the relative standing of the different groups, since it shows us that certain features, permanent in the lower groups, are transient in the higher ones. A striking instance of this occurs in the fact mentioned above, that though the long tentacles so characteristic of the adult Pleurobrachia exist in the young Bolina, they yield in importance at a later period to the lobes which eventually become the predominant and characteristic feature of the latter.

DISCOPHORae.

The disk of the Discophorae is by no means so delicate as that of the other Jelly-fishes. It seems indeed quite solid, and somewhat like cartilage to the touch, and yet so large a part of its bulk consists of water, that a Cyanea, weighing when alive about thirty-four pounds, being left to dry in the sun for some days, was found to have lost about 99/100 of its original weight,--only the merest film remaining on the paper upon which it had been laid. The prominence of the disk in this group of Jelly-fishes is well characterized by their German name, "Scheiben quallen," viz. disk-medusae. We shall see hereafter that the disk, so large and seemingly solid in the Discophorae, thins out in many of the other Jelly-fishes, and becomes exceedingly concave. This is especially the case in many of the Hydroid Medusae, where it a.s.sumes a bell-shaped form, and is constantly spoken of as the bell. It should be remembered, however, in reading descriptions of these animals, that the so-called bell is only a modified disk, and perfectly h.o.m.ologous with that organ in the Discophorae.

The Discophorous Medusae are distinguished from all others by the peculiar nature of the reproductive organs. They are contained in pouches (Fig. 50, _o_, _o_, _o_, _o_), the contents of which are first discharged into the main cavity, and then pa.s.s out through the mouth.

Pillars support the four angles of the digestive cavity, thus separating the lower from the upper floor of the disk, while the chymiferous tubes (Fig. 50) branch and run into each other near the periphery, forming a more or less complicated anastomosing network, instead of a simple circular tube, as is the case with the Hydroid Medusae. (Fig. 74.)

_Cyanea_. (_Cyanea arctica_ PeR. et LES.)

In our descriptions of the Discophorae, we may give the precedence to the Cyanea on account of its size. This giant among Jelly-fishes is represented in Fig. 44. It is much to be regretted that these animals, when they are not so small as to escape attention altogether, are usually seen out of their native element, thrown dead or dying on the sh.o.r.e, a ma.s.s of decaying gelatinous matter. All persons who have lived near the sea are familiar with the so-called Sea-blubbers, sometimes strewing the sandy beaches after the autumn storms in such numbers that it is difficult to avoid them in walking or driving. In such a condition the Cyanea is far from being an attractive object; to form an idea of his true appearance, one must meet him as he swims along at midday, rather lazily withal, his huge semi-transparent disk, with its flexible lobed margin, glittering in the sun, and his tentacles floating to a distance of many yards behind him.

Encountering one of those huge Jelly-fishes, when out in a row-boat one day, we attempted to make a rough measurement of his dimensions upon the spot. He was lying quietly near the surface, and did not seem in the least disturbed by the proceeding, but allowed the oar, eight feet in length, to be laid across the disk, which proved to be about seven feet in diameter. Backing the boat slowly along the line of the tentacles, which were floating at their utmost extension behind him, we then measured these in the same manner, and found them to be rather more than fourteen times the length of the oar, thus covering a s.p.a.ce of some hundred and twelve feet. This sounds so marvellous that it may be taken as an exaggeration; but though such an estimate could not of course be absolutely accurate, yet the facts are rather understated than overstated in the dimensions here given. And, indeed, the observation was more careful and precise than the circ.u.mstances would lead one to suppose, for the creature lay as quietly, while his measure was taken, as if he had intended to give every facility for the operation. This specimen was, however, of unusual size; they more commonly measure from three to five feet across the disk, while the tentacles may be thirty or forty feet long. The tentacles are exceedingly numerous (see Fig. 44), arising in eight distinct bunches, from the margin of the disk, and hanging down in a complete labyrinth.

These animals are not so harmless as it would seem, from their soft, gelatinous consistency; it is no pleasant thing when swimming or bathing to become entangled in this forest of fine feelers, for they have a stinging property like nettles, and may render a person almost insensible, partly from pain, and partly from a numbness produced by their contact, before he is able to free himself from the network in which he is caught. The weapons by which they produce these results seem so insignificant, that one cannot but wonder at their power. The tentacles are covered by minute cells, la.s.so-cells as they are called, (similar to those of Astrangia, Fig. 19,) each one of which contains a whip finer than the finest thread, coiled in a spiral within it.

[Ill.u.s.tration: Fig. 44. Cyanea arctica; greatly reduced in size.]

These myriad whips can be thrown out at the will of the animal, and really form an efficient galvanic battery. Behind the veil of tentacles, and partly hidden by it, four curtains, with lobed or ruffled margins, dimly seen in Fig. 44, hang down from the under surface of the disk. The ovaries are formed by four pendent pouches, placed near the sides of the mouth, and attached to four cavities within the disk. Around the circ.u.mference of the disk are eight eye-specks, each formed by a small tube protected under a little lappet or hood rising from the upper surface of the disk. The prevailing color of this huge Jelly-fish is a dark brownish-red, with a light, milk-white margin, tinged with blue, the tentacles and other pendent appendages having a somewhat different hue from the disk. The ovaries are flesh-colored, the curtain formed by the expansion of the lobes of the mouth is dark brown, while the tentacles are of different colors, some being yellow, others purple, and others reddish brown or pink.

[Ill.u.s.tration: Fig. 45. Scyphistoma of a Discoph.o.r.e; Aurelia flavidula. (_Aga.s.siz_.)]

[Ill.u.s.tration: Fig. 47. Strobila of a Discoph.o.r.e; Aurelia flavidula. (_Aga.s.siz_.)]

[Ill.u.s.tration: Fig. 46. Scyphistoma, older than Fig. 45.

(_Aga.s.siz_.)]

Strange to say, this gigantic Discoph.o.r.e is produced by a Hydroid measuring not more than half an inch in height when full grown; could we follow the history of any egg laid by one of these Discophorae in the autumn, and this has indeed been partially done, we should see that, like any other planula, the young hatched from the egg is at first spherical, but presently becomes pear-shaped, and attaches itself to the ground. From the upper end tentacles project (see Fig.

45), growing more numerous, as in Fig. 46, though they never exceed sixteen in number. As it increases in height constrictions take place at different distances along its length, every such constriction being lobed around its margin, till at last it looks like a pile of scalloped saucers or disks strung together (see Fig. 47). The topmost of these disks falls off and dies; but all the others separate by the deepening of the constrictions, and swim off as little free disks (Fig. 48), which eventually grow into the enormous Jelly-fish described above. These three phases of growth, before the relation between them was understood, have been mistaken for distinct animals, and described as such under the names of Scyphistoma, Strobila, and Ephyra.

[Ill.u.s.tration: Fig. 48. Ephyra of a Discoph.o.r.e; Aurelia flavidula.

(_Aga.s.siz_.)]

_Aurelia_. (_Aurelia flavidula_ PeR. et LES.)

[Ill.u.s.tration: Fig. 49. Aurelia seen in profile, reduced.

(_Aga.s.siz_.)]

Another large Discoph.o.r.e, though by no means to be compared to the Cyanea in size, is our common Aurelia (Figs. 49, 50) Its bluish-white disk measures from twelve to fifteen inches in diameter, but its dimensions are not increased by the tentacles, which have no great power of contraction and expansion, and form a short fringe around its margin, widening and narrowing slightly as the tentacles are stretched or drawn in. It is quite transparent, as may be seen in Fig 49, where all the fine ramifications of the chymiferous tubes as well as the ovaries, are seen through the vault of the disk. Fig. 50 represents the upper surface, with the ovaries around the mouth, occupying the same position as those of the Cyanea, though they differ from the latter in their greater rigidity, and do not hang down in the form of pouches. The males and females in this kind of Jelly-fish may be distinguished by the difference of color in the reproductive organs, which are rose-colored in the males, and of a dull yellow in the females. The process of development is exactly the same in the Aurelia as in the Cyanea, though there is a very slight difference in their respective Hydroids. They are, however, so much alike, that one is here made to serve for both, the above figures being taken from the Hydroid of the Aurelia. It is curious, that while, as in the case of the Aurelia and Cyanea, very dissimilar Jelly-fishes may arise from almost identical Hydroids, we have the reverse of the proposition, in the fact that Hydroids of an entirely distinct character may produce similar Jelly-fishes.

[Ill.u.s.tration: Fig. 50. Aurelia flavidula, seen from above; _o_ mouth, _e e e e_ eyes, _m m m m_ lobes of the mouth, _o o o o_ ovaries, _t t t t_ tentacles, _w w_ ramified tubes. (_Aga.s.siz_.)]

The embryos or little planulae, hatched from the Cyanea and Aurelia in the fall, seem to be gregarious in their mode of life, swimming about together in great numbers till they find a suitable point of attachment, and a.s.sume their fixed Hydroid existence. The Cyaneae, however, when adult, are usually found singly, while the Aureliae, on the contrary, seek each other, and commonly herd together.

_The Campanella_. (_Campanella pachyderma_ A. AG.)

[Ill.u.s.tration: Fig. 51. Campanella seen in profile; greatly magnified.]

[Ill.u.s.tration: Fig. 52. Same, seen from below.]

The Campanella (Fig. 51) is a pretty little Jelly-fish, not larger than a pin's head, reproduced directly from eggs, without pa.s.sing through the Hydroid stage. During its early stages of growth it probably remains attached to floating animals, thus leading a kind of parasitic existence; but as its habits are not accurately known, this cannot be a.s.serted as a constant fact respecting them. The veil in this Jelly-fish is very large, forming pendent pouches hanging from the circular ca.n.a.l (see Fig. 51), and leaving but just room enough for the pa.s.sage of the proboscis between the folds. It may not be amiss to introduce here a general account of this organ, which occurs in many of the Medusae, though it has very different proportions in the various kinds. It is a delicate membrane, hanging from the circular tube, so as partially to close the mouth of the bell, leaving a larger or smaller opening for the pa.s.sage of the water, which is taken in and forced out again by the alternate expansions and contractions of the bell.

There are but four chymiferous tubes in the Campanella, and four stiff tentacles, which in consequence of the peculiar character of the veil appear, when the animal is seen in profile, to start from the middle of the disk. The ovaries consist of eight pouches, placed near the point of junction of the four chymiferous tubes. (Fig. 52.) This little Medusa is of a dark yellowish color with brownish ocellated spots, scattered profusely over the upper part of the disk.

_Circe_. (_Trachynema digitale_ A. AG.)

[Ill.u.s.tration: Fig. 53. Trachynema digitale; about twice the natural size.]

Among the Jelly-fishes, the position of which is somewhat doubtful, is the Circe (Fig. 53), differing greatly in outline from the ordinary Jelly-fishes. As may be seen in Figure 53, the bell forms but a small portion of the animal; it rises in a sharp cone on the summit, thinning out at the lower edge, to form the large cavity in which hangs the long proboscis and the eight ovaries, four of which may be seen in Fig. 53 crowded with eggs. The Circe differs in consistency, as well as in form, from other Jelly-fishes. It is hard and h.o.r.n.y to the touch, and the veil, usually so light and filmy, is here a thick folded membrane, which at every stroke of the animal forces the water in and out of the cavity. It is very active, moving by powerful jerks, each one of which throws it far on its way. It advances usually in straight lines; or, if it wishes to change its direction, it drives the water out of the veil suddenly on one side or the other, so as to shoot off, sometimes at right angles with its former path. Four large pedunculated eyes, hidden in the figure by the tentacles, stand out prominently from the circular tube. When the animal is in motion, the tentacles are carried closely curled around the edge of the disk, as in Fig. 53, where the Circe is represented under a magnifying power of two and a half diameters. This Jelly-fish is of a delicate rose color, the tentacles a.s.suming, however, a dark-purple tint at their extremities when contracted.

_Lucernaria_. (_Haliclystus auricula_ CLARK.)

[Ill.u.s.tration: Fig. 54. Group of Lucernaria attached to eel-gra.s.s; natural size.]

[Ill.u.s.tration: Fig. 55. Lucernaria seen from the mouth side.]

One of the prettiest and most graceful, as well as one of the most common of our Jelly-fishes, is the Lucernaria (Fig. 54). It has such an extraordinary contractility of all its parts, that it is not easy to describe it under any definite form or position, since both are constantly changing; but perhaps of all its various att.i.tudes and outlines none are more normal to it than those given in Fig. 54. It frequently raises itself in the upright position represented here by the individual highest on the stem, spreading itself in the form of a perfectly symmetrical cup or vase, the margin of which is indented by a succession of inverted scallops, the point of junction between every two scallops being crowned by a tuft of tentacles. But watch it for a while, and the sides of this vase turn backward, spreading completely open, till they present the whole inner surface, with the edges even curved a little downward, drooping slightly, and the proboscis rising in the centre. In such an att.i.tude one may trace with ease the shape of the mouth, the lobes surrounding it, as well as the tubes and cavities radiating from it toward the margin. A touch is, however, sufficient to make it close upon itself, shrinking together in the att.i.tude of the third individual in Fig. 54, or even drawing its tentacles completely in, and contracting all its parts till it looks like a little ball hanging on the stem. These are but a few of its manifold changes, for it may be seen in every phase of expansion and contraction. Let us now look for a moment at the details of its structure. The resemblance to a cup or vase, as in the upper figure of the wood-cut (Fig. 54), is deceptive; for a vase is hollow, whereas the Lucernaria, though so delicate and transparent that its upper surface, when thus stretched, seems like a mere film, is nevertheless a solid gelatinous ma.s.s, traversed by certain channels, cavities, and part.i.tions, but otherwise continuous throughout. The peduncle by which it is attached is but an extension of the floor of a gelatinous disk, corresponding to that of any Jelly-fish. Four tubes pa.s.s through the whole length of this peduncle, and open into four chambers, dividing the digestive cavity above into as many equal s.p.a.ces. (Fig. 55.) These s.p.a.ces are produced by folds in the upper floor of the disk, uniting it to the lower floor at given distances, and forming so many part.i.tion-walls, dividing the digestive sac into four distinct cavities. These lines of juncture between the two floors, where the part.i.tions occur, produce the four radiating lines, running from the proboscis to the margin of the disk, on the upper surface. (Fig. 55.) The triangular figures, running from the mouth to each cl.u.s.ter of tentacles, are produced by the ovaries, which consist of distinct pouches or bags attached to the upper surface of the disk, and hanging down into the cavities below; every little dot within these triangular s.p.a.ces represents such a bag. Each bag is crowded with eggs, which drop into the digestive cavity at the sp.a.w.ning season, and are pa.s.sed out at the mouth. The tentacles always grow in cl.u.s.ters, but are nevertheless arranged according to a regular order. They are club-shaped at their extremities, but are hollow throughout, opening into the chambers of the digestive cavity, two of the cl.u.s.ters thus being connected with each chamber. Their chief office seems to be to catch the food and convey it to the mouth, though they may also be used as a kind of suckers, and the animal not unfrequently attaches itself by means of these appendages. Between every two cl.u.s.ters of tentacles will be observed a short, single appendage, of an entirely different appearance. These are the so-called auricles, and though so unlike tentacles in the adult animal, when in their earlier stages (Fig. 56) they resemble each other closely. But as their development goes on, the tentacles stretch out into longer, more delicate flexible organs, while the auricles remain short and compact throughout life.

They contain a slight pigment spot representing an eye, though how far it serves the purpose of vision remains doubtful. They are chiefly used by the animal as a means of adhering to any surface upon which it may wish to fasten itself; for the Lucernaria, though usually found attached to eel-gra.s.s in shoal water, has the power of independent motion, and frequently separates from its resting-place, floating about freely in the water for a while, or attaching itself anew by means of the auricles and tentacles upon some other object. The color of this pretty Acaleph varies from a greenish hue to green, with a faint tinge of red, or to a reddish brown. One of its commonest and most exquisite tints is that of a pale aqua-marine. It may be found along our sh.o.r.es wherever the eel-gra.s.s grows, and as far out as this plant extends. It thrives admirably in confinement, and for this reason is especially adapted to the aquarium.

[Ill.u.s.tration: Fig. 56. Young Lucernaria; magnified.]