During a recent cruise in the West Indies I had the opportunity of closely observing the Portuguese man-of-war, one of the most remarkable and most interesting of the ocean's inhabitants.
I had long felt a curiosity to examine for myself this little animal, regarding which I had read such varied and conflicting descriptions, and of whose nature nearly every naturalist seems to have formed a conception of his own. The Physalia, as the animal is known in scientific nomenclature, has, according to one author, the power of changing its color at will; another states that its colors are opaline or iridescent; and there are others, finally, who say that the colors are permanent or pigmental. In some figures the animal is represented with tentacles bearing discoid suckers like those oi 2i poulpe or cuttlefish, and by their side peculiar leaf-like appendages, the use of which does not seem to be clearly explained. It is also described as having, at the extremity of its vesicle or “bladder," a minute orifice for the admission and expulsion of air, with which the bladder is filled, and to which the animal owes its buoyancy. All descriptions which I have read unite in the statement that its stinging powers lie in the large mass of fleshy tentacles which extend from the keel of the little
"Man-of-war."
The Portuguese man-of-war consists of an elastic cylindrical airbladder, from eight to twelve inches in length and three or four inches in diameter. This tapers at each end to a point, one end being much more attenuated than the other, and apparently constituting the bow of the craft. This bow can be elongated or contracted at will, elevated, depressed, or moved laterally in any direction, like the proboscis of an elephant. Knowing that authors differed as to whether there was an orifice in the bow, I examined it carefully under a powerful magnifying glass, and found, not an orifice, but a dimple or umbilicus, around which the elastic tissue of the bladder is arranged in concentric rings. Comparing the animal to a ship, and using corresponding terms in its description, the bottom and bow are of a deep indigo color, blending into a lighter blue along the bilges, and to a faint lilac on the sides, above which it becomes almost perfectly transparent. Along its upper surface the bladder rises into a crest which has a slight resemblance to a lateen sail. This crest is simply a continuation of the bladder, forming with it a single air-chamber. Its cross-section is A-shaped, and is divided into eleven folds or segments by transverse membranes, as shown in the figure. The tip of the crest is edged with a beautiful frill of a delicate rose color, which is highly contractile, and by means of which the sail is taken in and folded over to the left.
From a fore-and-aft line, corresponding to the keel of a vessel, extend a mass of fleshy tentacles varying in length from a few inches to fifteen feet. These tentacles are of three classes, performing the offices respectively of nutrition, reproduction, and propulsion. They are united in sets to the bladder by means of short translucent tubes, each tube bearing tentacles of the three classes. They do not bear anything resembling suckers but have each, in a longitudinal line, a purple fold or frill as shown in c. Specimens of this frill when examined under the microscope showed that it consisted of large pigmented cells, covered with smaller cells as shown at a. Under 600 diameters these smaller cells proved to be nematocysts or thread-cells, as shown at b. These consist of a simple cell in which there is a coiled spiral thread which is highly elastic. Under the slightest pressure the spiral straightens itself out, extending through the cell-wall, and penetrating its victim with the sharp barbed point, which remains in the wound.
Knowing the animal's stinging powers, I was very careful not to allow my hand to come in contact with its tentacles; but what was my unpleasant surprise when on touching the lower surface of its bow, in examining the alleged orifice, to feel a burning sensation so intense that it seemed as though my hand had touched a red-hot coal. This was communicated to my cheek, which I accidentally touched with my hand, and the pain continued for more than twelve hours. On examination I found that the whole lower surface of the body contained multitudes of thread-cells, of a smaller size, however, than those of the tentacles. When I would seize it by the crest, the little animal would turn over on its side and raise its proboscis to my hand as though attempting to sting it.
It was impossible for me to conceive the Physalia to be a colony of individuals, as is held by eminent naturalists. It would swim around the margin of its prison, carefully touching every point with
its proboscis, at times raising it several inches above the surface, as though seeking to escape. Then it would fall back and writhe as if in despair. It is true that it does possess many sets of mouths, pro-pellers, and organs of reproduction; yet we must remember that its organization is even lower than that of a mollusc; and may it not be nourished as a plant is nourished? A creeping plant is an individual, and yet it receives its nourishment from a hundred sets of rootlets, and it may bear any number of flowers possessing perfect ovaries. And just as the plant may be propagated by cuttings, so may the Physalia reproduce by gemmation or budding.
The bladder of the Physalia is double-walled; that is, it consists of two membranes, one fitting tightly within the other as a rubber football fits within its cover; but the use of the second membrane does not seem to have been understood by any of the writers whose descriptions I have read. With a sharp needle I pierced the bladder, thrusting it fully an inch through the two membranes. On withdrawing it, the wonderful part which the second membrane played in the economy of the animal was revealed. The orifice was closed almost instantly by the sliding of the outer membrane upon the inner, through the space of about the tenth of an inch, thus interrupting the coincidence of the punctures in the outer and the inner membranes.
Again and again I pierced the bladder, but every time the puncture was closed as promptly as before; and not even by thrusting the animal below the surface with a forked stick could I cause it to part with a bubble of air. Were it not for this happy faculty of closing small punctures in its bladder, the slightest wound from the spine of a fish or an echinoderm would be sufficient to make it collapse
and sink to the bottom.
In conclusion I would say that naval officers often have excellent opportunities for observing animals whose habits are as yet unknown to the naturalist ; such, for instance, as many pteropod molluscs, the beautiful Argonaut, and the little glassy Vellela. And not only may they be the means of contributing to the natural history of the globe; but to those whose life is spent upon the surface of the ocean, the study of the wonderful and varied forms of the life within its depths cannot but prove intensely interesting.
DISCUSSION.
p. AssT. Surgeon D. N. Bertolette.—While the double wall of the air-bladder or pneumatocyst may aid in preventing the escape of air from accidental punctures, it is not absolutely necessary that the membrane should be doubled to obtain the same result. When a fibrous membrane is pierced by a smooth slender instrument such as an ordinary sewing needle, the fibres are not ruptured or torn, but merely separated until the withdrawal of the foreign body, when their elasticity brings them back to their former position, and what was a theoretical opening is now practically closed. This observation refers only to punctures of very small diameter. The circular fibres surrounding the dimple where Mr. Safford looked for the opening connecting the air-vesicle with the air were possibly a sort of sphincter muscle controlling this opening. These muscles closing the opening with a spasm probably accounts for the lecturer's want of success in discovering it. Nearly all the congeners of the Physalia have these
openings, or stigmata, communications between the cyst and the open air, and it is most probable that the Portuguese Man-of-War is similarly supplied.
The Cnidae, nematocysts or thread-cells are peculiar structures common to the Coelenterata. They consist of small oval cells tensely filled with fluid, and containing a spirally coiled filament barbed at its base and finely serrated along the sides. Upon the slightest pressure these cells rupture and the filament is suddenly uncoiled, projecting a considerable distance. While even in the more minute Hydra these cells have some benumbing and deleterious influence upon animal organisms captured as prey, still comparatively few have the power of puncturing the human skin. Mr. Safford's observation that he had produced pain in his cheek by touching it with a finger which had been stung by a Physalia is possibly new, and is certainly worth further investigation.
Midshipman W. E. Safford.—In reply to Dr. Bertolette, I would say that the needle which I used in piercing the vesicle was so coarse as to cause an orifice perceptible to the naked eye, and the punctures of the inner and the outer membranes were distinctly visible after their coincidence had been interrupted, the inner one showing through the outer membrane about the tenth of an inch from the outer puncture. All observers seem to unite in remarking that there are no muscles whatever
in the vesicle of the Physalia, and it was only after carefully examining a thin section of the membrane around the "umbilicus," that I concluded there was no orifice at that point. Professor Huxley in his "Anatomy of Invertebrates" does not mention such an opening, nor does Professor Agassiz, in his "Contributions to the Natural History of the United States," in which he gives an excellent description of the animal.
Regarding the animal's stinging powers, M. Gervais says of a sufferer: " Qu'un vase qui avait renferm^ line physalie vivante ti''ayant pas ^te suffisamment nettoy/, il se brilla les Vevres^ le nez et les jones en se servant de ce vase pour se laver."