The Cubomedusæ E-Book

Franklin Story Conant

• Herausgeber: Franklin Story Conant
• Kategorie: Lebensstil
• Sprache: Englisch

Veröffentlichungsjahr: 2017

Beschreibung

Jelly-fish offer to the lover of natural history an inexhaustible store of beauty and attractiveness. One who has studied them finds within him a ready echo to Haeckel’s statement that when first he visited the seacoast and was introduced to the enchanted world of marine life, none of the forms that he then saw alive for the first time exercised so powerful an attraction upon him as the Medusæ. The writer counts it a rare stroke of fortune that he was led to the study of a portion of the group by the discovery of two new species of Cubomedusæ in Kingston Harbor, Jamaica, W. I., while he was with the Johns Hopkins Marine Laboratory in June of 1896.
The Cubomedusæ are of more than passing interest among jelly-fish, both because of their comparative rarity and because of the high degree of development attained by their nervous system. One fact alone suffices to attract at once the attention of the student of comparative morphology—that here among the lowly-organized Cœlenterates we find an animal with eyes composed of a cellular lens contained in a pigmented retinal cup, in its essentials analogous to the vertebrate structure. Perhaps this and other facts about the Cubomedusæ would be more generally known, had they not been to a certain extent hidden away in Claus’s paper on Charybdea marsupialis (’78), which, while a record of careful and accurate work, is in many respects written and illustrated so obscurely that it is very doubtful whether one could arrive at a clear understanding of its meaning who was not pretty well acquainted with Charybdea beforehand.

Leseprobe

Franklin Story Conant

The Cubomedusæ

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Table of contents

A BIOGRAPHICAL SKETCH

LIST OF THE PUBLISHED BIOLOGICAL PAPERS OF FRANKLIN STORY CONANT.

INTRODUCTION.

Part I: SYSTEMATIC.

Part II: GENERAL DESCRIPTION OF THE ANATOMY OF THE CUBOMEDUSÆ.

Part III: DESCRIPTION OF SPECIAL PARTS OF THE ANATOMY.

LITERATURE REFERRED TO.

TABLE OF REFERENCE LETTERS.

DESCRIPTION OF FIGURES.

A BIOGRAPHICAL SKETCH

Franklin Story Conant was born in Boston on September 21, 1870, and he died in Boston on September 13, 1897, a few days after his arrival from Jamaica, where he had contracted yellow fever through self-sacrificing devotion to others.He was educated in the public schools of New England; at the University of South Carolina; at Williams College, where he received the degree of Bachelor of Arts in 1893; and in the Johns Hopkins University, where he received the degree of Doctor of Philosophy in 1897, and where he was appointed a Fellow in 1896 and Adam T. Bruce Fellow in 1897.Most of his instructors have told us that they quickly discovered that Conant was a young man of unusual intelligence and energy and uprightness, and as his education progressed he secured the esteem and the affectionate interest of all who had him in charge, so that they continued to watch his career with increasing pride and satisfaction.He entered the Johns Hopkins University in the spring of 1894, and at once joined the party of students in zoology who were working, under my direction, in the marine laboratory of the University at Beaufort, North Carolina; and from that time until his death he devoted himself continually, without interruption, to his chosen subject—spending his winters in the laboratory in Baltimore, and devoting his summers to out-of-door studies at Beaufort and at Wood’s Holl, and in Jamaica.It is as a student and not as an investigator that we most remember Conant, for most of his time was given to reading and study on subjects of general educational value; although he had begun, before his death, to make original contributions to science and to demonstrate his ability to think and work on independent lines.His study of the Chaetognaths was undertaken only for the purpose of verifying the account of their anatomy and development in the text books, but it soon showed the presence at Beaufort of several undescribed species. Without interrupting his more general studies, he employed his odd moments for three years in their systematic analysis, and at last published two papers, “Description of Two New Chaetognaths,” and “Notes on the Chaetognaths,” which show notable power of close and accurate observation and of exact description; and, while short, are valuable contributions to our knowledge of this widely distributed but difficult group.As he appreciated the value to one who has devoted himself to zoology of thorough acquaintance with physiological problems and the means for solving them, he wished, after he had completed his general course in physiology, to attempt original research in this field; and, at the suggestion of Professor Howell, he, in company with H. L. Clark, his fellow student, undertook and successfully completed an investigation of which Professor Howell gives the following account:In connection with Mr. H. L. Clark, Mr. Conant undertook to investigate the character of the nervous control of the heart beat in decapod crustaceans. They selected the common edible crab, Callinectes hastatus, and made a series of most careful experiments and dissections which resulted in proving the existence of one inhibitory nerve and two accelerator nerves passing to the heart on each side from the thoracic ganglion. They not only demonstrated the physiological reaction of these nerves, but traced out successfully their anatomical course from the ganglion to the pericardial plexus. It seemed hardly probable from an a priori standpoint that in an animal like the crab there should be any necessity for an elaborate nervous mechanism to regulate the beat of the heart, but their experiments placed the matter beyond any doubt, and have since served to call attention to this animal as a promising organism for the study of some of the fundamental problems in the physiology of the heart. As compared with previous work upon the same subject it may be said that their experiments are the most definite and successful that have yet been made.His chief completed work, the Dissertation on The Cubomedusæ, is here printed; and through it the reader who did not know Conant must decide whether he was well fitted, by training and by natural endowments, for advancing knowledge. I myself felt confident that the career on which he had entered would be full of usefulness and honor. I was delighted when he was appointed to the Adam T. Bruce Fellowship, for I had discovered that he was rapidly becoming an inspiring influence among his fellow students in the laboratory, and I had hoped that we might have him among us for many years, and that we might enjoy and profit by the riper fruits of his more mature labors.Immediately after his examination for the degree of Doctor of Philosophy in June, 1897, he set out for Jamaica to continue his studies at the laboratory which this University had established for the summer at Port Antonio, and he there worked for nearly three months on the development, and on the physiology of the sense-organs, of the Cubomedusæ.His notes and specimens are so complete that I hope it will be possible to complete in Baltimore, at an early day, the work which he had expected to carry on this year.After the sudden and alarming death of the director of the expedition, Dr. J. E. Humphrey, Conant took the burden of responsibility upon himself, and while he fully appreciated his own great danger, he devoted himself calmly and methodically to the service of others who, in their afflictions, needed his help, and he fell in the path of duty, where he had always walked, leaving behind him a clear and simple account of all the business of the laboratory and of his scientific work, and of his own affairs, complete to the day before his death.Immediately after the opening of the University in October his friends and companions and instructors assembled to express the sorrow with which they had heard the sad news of his death, and to record their love and esteem for the generous, warm-hearted friend who in all the relations of life had proved himself so worthy of their affectionate remembrance. At this meeting those who had worked at his side in our laboratories recalled his steadfast earnestness in the pursuit of knowledge, and the encouragement they had found in his bright example; while those who had been his instructors spoke of him as one who had bettered their instruction and enriched all that he undertook by sound and valuable observations and reflections. While all united in mourning the untimely loss of one who had shown such rich promise of a life full of usefulness and honor and distinction, it was pointed out with pride that his end was worthy of one who had devoted it to the fearless pursuit of truth, and to generous self-sacrifice and noble devotion to others; and it was resolved, “That we prize the lesson of the noble life and death of Franklin Story Conant.”

LIST OF THE PUBLISHED BIOLOGICAL PAPERS OF FRANKLIN STORY CONANT.

1. Description of Two New Chaetognaths. Johns Hopkins University Circulars, No. 119, June, 1895.2. Notes on the Chaetognaths. Johns Hopkins University Circulars, No. 126, June, 1896.3. The Inhibitory and Accelerator Nerves to the Crab’s Heart (an abstract), by F. S. Conant and H. L. Clark. Johns Hopkins University Circulars, No. 126, June, 1896.4. On the Accelerator and Inhibitory Nerves to the Crab’s Heart, by F. S. Conant and H. L. Clark. The Journal of Experimental Medicine, Vol. I, No. 2, 1896.5. Notes on the Cubomedusæ (an abstract). Johns Hopkins University Circulars, No. 132, November, 1897.6. The Cubomedusæ.

INTRODUCTION.

Jelly-fish offer to the lover of natural history an inexhaustible store of beauty and attractiveness. One who has studied them finds within him a ready echo to Haeckel’s statement that when first he visited the seacoast and was introduced to the enchanted world of marine life, none of the forms that he then saw alive for the first time exercised so powerful an attraction upon him as the Medusæ. The writer counts it a rare stroke of fortune that he was led to the study of a portion of the group by the discovery of two new species of Cubomedusæ in Kingston Harbor, Jamaica, W. I., while he was with the Johns Hopkins Marine Laboratory in June of 1896.The Cubomedusæ are of more than passing interest among jelly-fish, both because of their comparative rarity and because of the high degree of development attained by their nervous system. One fact alone suffices to attract at once the attention of the student of comparative morphology—that here among the lowly-organized Cœlenterates we find an animal with eyes composed of a cellular lens contained in a pigmented retinal cup, in its essentials analogous to the vertebrate structure. Perhaps this and other facts about the Cubomedusæ would be more generally known, had they not been to a certain extent hidden away in Claus’s paper on Charybdea marsupialis (’78), which, while a record of careful and accurate work, is in many respects written and illustrated so obscurely that it is very doubtful whether one could arrive at a clear understanding of its meaning who was not pretty well acquainted with Charybdea beforehand.Before Claus’s paper was received at this laboratory, H. V. Wilson went over essentially the same ground upon a species of Chiropsalmus taken at Beaufort, N. C. When the article on Charybdea marsupialis appeared, however, the results were so similar that Wilson did not complete for publication the careful notes and drawings he had made.Haeckel’s treatment of the Cubomedusæ in his “System” (’79) in the Challenger Report (’81) is much more lucid than Claus’s; but the extended scope of his work and the imperfect preservation of his material prevented a detailed investigation, and for a more complete and readily intelligible account of the structure of the Cubomedusæ a larger number of figures is desirable.In the foregoing facts lies whatever excuse is necessary for repeating in the present paper much that has already seen print in one form or another.

Part I: SYSTEMATIC.

It seems advisable first of all to establish the systematic position of the two newly found species, Charybdea Xaymacana and Tripedalia cystophora. Haeckel’s classification, as given in his “System der Medusen,” is an excellent one and will be followed in this case. One of the new species, however, will not classify under either of Haeckel’s two families, so that for it a new family has been formed and named the Tripedalidæ. In showing the systematic position of the two new forms, an outline of Haeckel’s classification will be given, so far as it concerns our species, together with the additions that have been made necessary.

Cubomedusæ (Haeckel, 1877).

Characteristics: Acraspeda with four perradial sensory clubs which contain an auditory club with endodermal otolith sac and one or several eyes. Four interradial tentacles or groups of tentacles. Stomach with four wide perradial rectangular pockets, which are separated by four long and narrow interradial septa, or cathammal plates. Gonads in four pairs, leaf-shaped, attached along one edge to the four interradial septa. They belong to the subumbrella, and are developed from the endoderm of the stomach pockets, so that they project freely into the spaces of the pockets.

Family I: Charybdea (Gegenbaur, 1856).

Cubomedusæ with four simple interradial tentacles; without marginal lobes in the velarium, but with eight marginal pockets; without pocket arms in the four stomach pockets.

Genus: Charybdea.

Charybdeidæ with four simple interradial tentacles with pedalia; with velarium suspended, with velar canals and four perradial frenula. Stomach flat and low, without broad suspensoria. Four horizontal groups of gastric filaments, simple or double, tuft or brush-shaped, limited to the interradial corners of the stomach.

Species: Charybdea Xaymacana (Fig. 1).

Bell a four-sided pyramid with the corners more rounded than angular, yet not so rounded as to make the umbrella bell-shaped. The sides of the pyramid parallel in the lower two-thirds of the bell, in the upper third curving inward to form the truncation; near the top a slight horizontal constriction. Stomach flat and shallow. Proboscis with four oral lobes, hanging down in bell cavity a distance of between one-third and one-half the height of bell; very sensitive and contractile, so that it can be inverted into the stomach. The four phacelli epaulette-shaped, springing from a single stalk. Distance of the sensory clubs from the bell margin one-seventh or one-eighth the height of bell. Velarium in breadth about one-seventh the diameter of the bell at its margin. Four velar canals in each quadrant; each canal forked at the ends, at times with more than two branches. Pedalia flat, scalpel-shaped, between one-third and one-half as long as the height of bell. The four tentacles, when extended, at least eight times longer than the bell. Sexes separate. Height of bell, 18-23 mm.; breadth, about 15 mm. (individuals with mature reproductive elements); without pigment. Found at Port Henderson, Kingston Harbor, Jamaica.

As may be seen from the above, C. Xaymacana differs only a little from the C. marsupialis of the Mediterranean. Claus mentions in the latter a more or less well defined asymmetry of the bell, which he connects with a supposed occasional attachment by the proboscis to algæ. In C. Xaymacana I never noticed but that the bell was perfectly symmetrical. C. Xaymacana is about two-thirds the size given by Claus for his examples of C. marsupialis, which were not then sexually mature. It has 16 velar canals instead of 24 (32), as given by Haeckel, or 24 as figured by Claus. Difference in size and in number of velar canals are essentially the characteristics upon which Haeckel founded his Challenger species, C. Murrayana.

Family II: Chirodropidæ (Haeckel, 1877).

Cubomedusæ with four interradial groups of tentacles; with sixteen marginal pockets in the marginal lobes of the velarium, and with eight pocket arms, belonging to the exumbrella, in the four stomach pockets.

This family is represented in American waters by a species of Chiropsalmus, identified by H. V. Wilson as C. quadrumanus, found at Beaufort, North Carolina.

Family III: Tripedalidæ (1897).

Cubomedusæ with four interradial groups of tentacles, each group having three tentacles carried by three distinct pedalia; without marginal lobes in the velarium; with sixteen marginal pockets; without pocket arms in the stomach pockets.

Genus: Tripedalia.

For the present the characteristics of family and genus must necessarily be for the most part the same. The genus is distinguished by having twelve tentacles in four interradial groups of three each; velarium suspended by four perradial frenula; canals in the velarium; stomach projecting somewhat convexly into the bell cavity, with relatively well-developed suspensoria; four horizontal groups of gastric filaments, each group brush-shaped, limited to the interradial corners of the stomach.

Species: Tripedalia cystophora (Fig. 17).

Shape of bell almost exactly that of a cube with rounded edges; the roof but little arched. The horizontal constriction commonly seen near the top of the bell in the Cubomedusæ not present. Proboscis with four oral lobes; hanging down in the bell cavity generally more than half the depth of the cavity and at times even to the bell margin. In the gelatine of the proboscis an irregular number (15-21) of sensory organs resembling otocysts, from the presence of which comes the specific name. Phacelli brush-shaped, composed of from seven to thirteen filaments springing from a single stalk in each quadrant, or rarely from two separate stalks in one of the quadrants. Distance of the sensory clubs from the bell margin about one-fifth or one-fourth of the height of bell. Breadth of velarium about one-sixth the diameter of bell at margin; with six velar canals in each quadrant; the canals simple, unforked. Pedalia flattened, shaped like a slender knife blade, about half as long as the height of the bell. Tentacles at greatest extension observed two and a half times the length of pedalia. Sexes separate. Height of bell in largest specimens (reproductive elements mature) eight or nine mm. Breadth same as height or even greater. Color a light yellowish brown, due in large part to eggs or embryos in the stomach pockets. The reproductive organs especially prominent by reason of their similar color. Found in Kingston Harbor, Jamaica.

It will be seen from the above that Tripedalia possesses two of the characteristics of the Charybdeidæ and two of the Chirodropidæ. The family was named from the prominent feature of the arrangement of the tentacles, in groups of three with separate pedalia. The small size of T. cystophora is worthy of note in connection with the fact that of the twenty species of Cubomedusæ given by Haeckel in his “System” only two are smaller than 20 mm. in height, and those are the two representatives of Haeckel’s genus Procharagma, the prototype form of the Cubomedusæ, without pedalia and without velarium. While Tripedalia has both pedalia and velarium, it may be perhaps that its small size, taken in connection with characteristics just about midway between the Charybdeidæ and the Chirodropidæ, indicate that it is not a recently acquired form of the Cubomedusæ.

Part II: GENERAL DESCRIPTION OF THE ANATOMY OF THE CUBOMEDUSÆ.

A:Charybdea Xaymacana.

a.Environment and habit of life.

1. The Cubomedusæ are generally believed to be inhabitants of deep water which come to the surface only occasionally. Both of the Jamaica species, however, were found at the surface of shallow water near the shore, and only under these circumstances. Whether these were their natural conditions, or whether the two forms were driven by some chance from the deep ocean [...]