F93.8 Return this book on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. 59 . 11 . 99:38 CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HAIiVARI) COLLEGE. E. L. MARK, Director. * v t 2 )' No. 1G3. ~flcdC^ phosphorescence: in ctenophores. By Amos W. Peters. From the Journal of Experimental Zoology, Vol. II, No. 1. CAMBRIDGE, MASS., U. S. A. April, 1905. I Digitized by the Internet Archive , in 2017 with funding from University of Illinois Urbana-Champaign Alternates I I (, i I https://archive.org/details/phosphorescenceiOOpete CONTRIBUTIONS FROM THF ZOOLOGICAL LABORATORY OF THK MUSKUM I OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, j Dirkctor. — No. 163. PHOSPHORESCENCE IN CTENOPHORES. liY AMOS PETERS. INTRODUCTION. The problems discussed in this paper are the localization of the power of phosphorescence in mature and in young ctenophores, nd the influence of certain factors, such as mechanical stimula- tion, light, and heat, upon the ability of these animals to phos- phoresce. The species upon which I have worked is the common summer ctenophore, Mnemiopsis leidyi A. Agassiz. These animals were to be found at Wood’s Hole, Mass., abundantly during August, 1902 and 1903. The phenomenon of phosphorescence which they exhibited in their native sea-water when mechanically agitated after dark was suggestive of laboratory experiments. In my experiments I found it necessary to use a dark chamber, which I constructed from a simple pine box heavily covered first ‘with paper and then with several layers of black cloth. The dark box was placed upon a table before the experimenter and its open front was provided with overhanging cloth, sufficient to include his head and shoulders. This arrangement permitted both the ^observation of phosphorescence and the free use of the experi- nienter’s hands for agitating the ctenophores, etc. This appara- tus was not quite as efficient as a dark room, yet it was adequate fc>r the work that- was attempted in it. As observation of the animals required the continuous attention of the experimenter in ,tl.e dark-box and as light must be excluded, the time was read and rr corded by an assistant upon signals from the experimenter. 1 his procedure also favored the adjustment of the experimenter’s eye to the conditions of observation after the change from daylight to darkness. The time here recorded was read to tenths of a minute, and differences so small as this are nowhere of conse- 104 Amos W. Peters. quence in the following work. The abundance ot the material made it possible to select animals of the same large size for most of the experiments. Lots of from four to eight were placed in glass or porcelain dishes containing about one liter of sea-water brought in with the animals. In these dishes most of the test s for phosphorescence were made. Several methods of mechanical stimulation, to be used in testing the animals for phosphorescence, were tried and compared. The most efficient of these was stirring the ctenophores by means of a glass rod. Simple contact with the rod frequently succeeded in bringing forth the response of phosphorescence when jarring, shaking, etc., failed. The adult animals being of sufficient size and weight, the contact of the glass rod with them was easily perceptible through the skin and muscles of the experimenter in the dark. This method of stimulation was uniformly adopted rs a standard in this work, being also used for small parts of animals, embryos, and eggs. Unless a statement to the contrary is mad(S a fresh, previously unused lot of ctenophores was used in eaca test. Strict uniformity of conditions and the constant presence of control animals excluded from the observations here recorded, it is hoped, errors arising from insufficient adjustment of the eye as well as from other sources. That these experiments could profitably be repeated and extended with a much grean^r degree of refinement, is a point the writer desires to emphasize. He wishes to express here his indebtedness to Dr. G. H. Parker, of Harvard University, for critical advice and suggestion, and for the revision of the manuscript. He is also under obligation to the Humboldt Fund of the Museum of Comparative Zoology at Harvard College for financial assistance. Furthermore, his thanks are due to the authorities of the United States Fish Com- mission for the use of its laboratory at Wood’s Hole, Mass., during the summers of 1902 and 1903. II. LOCALIZATION OF PHOSPHORESCENCE. I. In Mature Animals. As is well known, ctenophores brought into the laboratory disintegrate quite readily. The dead substance of such animrls was frequently tested both in the dark-hox and in the dark-room Phosphorrscriice in (Jfcnophores. 105 In no case was any phospliorescence detected in the dead matter originating from ctenopliores. It was observed that after rough weather many ctenophores were mutilated hut nevertheless phosphorescent. Even separated pC)rtions of the animal show this reaction both in the sea and in the laooratory. Such pieces examined under the magnifier always showed movements of the paddle plates and frequently muscular contraction. In short, the pieces of the animal were found to be alve. All the observations made gave the result that only the In ing ctenophores or living parts of them phosphoresce. When either whole ctenophores of small size, or, much better, excised parts from various regions of the animal were examined under the magnifier in the dark, phosphorescence seems to be piesent only along the rows of paddle plates. When the paddle pi ites were numerous upon the excised piece, adjacent parts were often so illuminated as to make this determination uncertain. But when portions of the jelly entirely free from paddle plates Were examined no phosphorescence was seen. Such jelly was alive, for when the same preparation was examined in the daylight muscular contraction could be seen in it. In the course of these experiments no phosphorescence could be obtained from jelly frqe from paddle plates. The smallest piece from which phosphorescence was obtained consisted of four connected paddle plates with, of course, some jelly adhering. Even single excised paddle plates were observed to live for many hours or a day, as judged by their motion, and yet; all efforts to get phosphorescence from single excised paddle plrtes were unsuccessful. The excised auricles showed, under the magnifier, cilia but no pjaddle plates. No phosphorescence was obtained from them. ^ ! The sense organ with adjacent parts was excised in a piece about two centimeters long and one centimeter broad. Under the uiagnifier no paddle plates were seen, but muscular contraction W as evident. No phosphorescence could be obtained from such a piece. The previously described experiments with excised rows of paddle plates, or parts of them, are sufficient to show that phos- phorescence does not depend upon correlation of the part with the simse organ. Whether cut in two transversely, or longitudinally ir such a manner as to leave the sense organ wholly in one part. io6 A mos fV. Peters. the result was the same. In both cases the piece without. the sense organ, as well as that with it, was phosphorescent. If the whole animal had been made phosphorescent in the dark- box before the operation, both pieces retained phosphorescence; if the whole animal was originally non-phosphorescent, the pieces acquired this property in the dark-box. Numerous tests were made to determine whether after trans- verse or longitudinal division the piece retaining the sense organ acquired phosphorescence sooner or later than the other piece. A normal animal, as a check, was subjected to the same test at the same time. The results seemed to follow the law of chance. Sometimes the piece with the sense organ phosphoresced more quickly than the other, sometimes more slowly. The results were hence negative and warrant the statement that the sense organ is not a controlling center for phosphorescence. It was now clear that phosphorescence was localized somewhere in or near the paddle plates, and that the reaction-chain from stimulation to response consists very probably of an anatomically short and entirely local series of elements, i. ^., there is no dista nt central station for the reception, modification, or dispatch of impulses. Although it was shown that phosphorescence bears a local relation to the paddle plates the question was still opc^n whether any necessary relation existed. The attempt was therefore made to ascertain by experime nt whether all movement of the paddle plates are accompanied w th phosphorescence. A glass evaporating dish eight .inches in diameter and three inches in depth was filled with sea-water to within half an inch of the top. At night a single medium-si; ed and strongly phosphorescent ctenophore was placed in the dish in the dark-room. The whole was left undisturbed for some time to insure the absence of currents originating from external me- chanical disturbance of the dish. At intervals the dark-room wrts sufficiently illuminated to enable the observer to note the position of the animal in the dish. During the dark periods the attention of the experimenter was directed upon the dish for the purpose of observing phosphorescence, if any occurred. The result was thot though the ctenophore was almost constantly changing position, sometimes to the extent of half the diameter of the dish, yet it showed no phosphorescence during the great majority of the dark intervals. Evidently during such intervals the paddle plates e 107 J^hosphorescnicr iii C'Jctiopborcs. in motion and yet without being accompanied by phosphorescence. When in a dark period phosj)liorescence was seen, the light was immediately turned on, and it was observed that the ctenophore was adjacent to the side of the dish and had probably struck it in the course of locomotion. A slight mechanical stimulus, such as touching the animal with a glass rod, jarring the dish, or the table upon which it was placed, easily elicited the response of phos- phorescence, both before and after the experiment described above. It was clear that the animal was capable of phosphores- cence during all the periods of locomotion, but the necessary mechanical stimulus was absent except when the ctenophore came into contact with the side of the dish. 2. In Embryos. Further observations were directed toward finding how far back in the ontogeny of the animal phosphorescence could be traced. The eggs were obtained as follows: On August 6, some ctenophores were brought into the laboratory and placed in glass evaporating dishes each containing about two liters of the sea- water brought in with them. Two animals were placed in each dish. The water was changed once or twice, only such being used as was brought directly from the sea. On the morning of August 7, a layer of eggs in various stages of development was found upon the bottom of each dish. By withdrawing the sea- water above them and replacing it with fresh sea-water about twice a day, they were reared to fully formed young ctenophores. In no instance were eggs observed to be deposited in the day time. When a lot of eggs had developed to the stage in which the four sets of paddle plates first appear, phosphorescence could be demonstrated. If at night the embryos were stirred with a glass rod, or the dish containing them was jarred, numerous phos- phorescent specks would appear momentarily. The experiment did not easily succeed in the day time, even if the eggs were kept in the dark-room. Perhaps the same rhythm in the intensity of phosphorescence belongs to them as to the adults. In the latter it was observed (1903) that phosphorescence was more intense and more easily excited at night than during the daytime, even when the animals were kept continuously in the dark-room. Furthermore, the phosphorescence of these embryos could not be indefinitely repeated, but was exhausted after a few flashes. In o8 A mos JV. Peters. this respect also they resemble the adults, except that exhaus:ion is much more quickly produced. Experiments were made to test for phosphorescence before the formation of the paddle plates. A single gastrula was isolated at night in a watch glass. It was still contained in the egg- capsule and showed ciliary movement but no paddle plates were as yet developed. It was placed in the dark-room and, to make the conditions as favorable for the reaction as possible, it was allowed to remain undisturbed for half an hour, when the watch glass was suddenly jarred and a flash resulted. Another flash could not be obtained until after a period of rest. Experiments were next made to test for phosphorescence in the segmentation stages and in the egg. It had been several times observed during these studies that embryos from animals that had been kept in the dark-room during the previous day were further advanced when examined the next morning than the embryos from animals kept in diffuse daylight during the previous day. Both lots originated from the same collection and were parallel in conditions except with regard to light. In this experiment the influence of light upon the time of egg laying was also tested. August II, 1903,2 p. m. Collected Mnemiopsis. Distribu ed them into lots A and B, each consisting of several dishes. A was kept in the dark-room. B remained in diffuse daylight, later in artificial light, electricity and gas. 10 p. m. No eggs. 1 1. 1 5 p. m. Eggs present in lot A of the dark-room. No eggs in lot B. A number of eggs were immediately isolated in a solid watch glass and tested by stirring with a glass rod and by jarring, at intervals, in the dark-room. They were examined before and after the series of tests and were found to consist of one-cell stages. No phosphorescence could be detected in these undivided eggs. August 12, 12.20 a. m. Cleavage stages from lot A were iso- lated in a solid watch glass. Examination before and after the tests showed that no ciliated (moving) embryo was as yet formc'd. Stages from one to thirty-two cells were present. After an undis- turbed period in the dark-room stirring with a glass rod elicited phosphorescent flashes, but probably not from all the eml-ryos. 12.45 ^gg^ Phosphorrscnicr in (Ucno pJjores . 1 09 1.20 a. ni. Many embryos in lot A were becoming gastrul^c. Also many undeveloped (dead ?) one-cell stages were still present in lot A. ^ 1.30 a. m. No eggs in lot B. 2.20 a. m. Some esss in lot B. Some of these were isolated in solid watch glasses, examined before and after testing for phosphorescence and found to be-in one-cell stages. 2.40 a. m. No phosphorescence was detected in the one-cell stao-e isolated above from lot B. An interesting result of this experiment is the difference of about three hours in the time of the laying of the eggs between lots A and B; lot A having been in the dark longer, deposited eggs sooner. In a subsequent experiment it was observed that animals kept in the dark from 9 a. m. had not yet deposited eggs at 10.30 p. rn., although eggs were present the next morning. Hence the deposition of eggs does not seem to occur after simply a given number of hours of darkness. The indications favor the view that the deposition of eggs takes place in accordance with the daily rhythm of light and darkness, deposition occurring in the dark period, and being capable of retardation by light. III. INFLUENCE OF CERTAIN FACTORS ON PHOSPHORESCENCE. I. Agitation and Light. In determining what factors influence phosphorescence it has been found convenient to deal with agitation and light together. Preliminary tests showed that ctenophores removed to the dark- box at once from their native sea-water, where they had been exposed to direct sunlight, were not immediately phosphorescent. However, they became so after remaining in the dark for some time. Similar observations were first made on Beroe by Allman (’62) and subsequently by Panceri (’72). The above fact was the starting point for a series of experiments in which both light and agitation were factors. Experiment I. Lots A and B having been exposed to direct sunlight for about one hour, were both placed in the dark-box at the same time. The ctenophores in A were then continually agitated with a glass rod, while B was left undisturbed except for momentary tests made at intervals. A phosphoresced first in 2.5 minutes; B in 3.0 minutes. 1 10 A mos fV. Peters. The result shows that direct sunlight prevents the occurrence of phosphorescence and that mechanical stimulation accelerates it. Experimej^t 2 . Two phosphorescent lots, A and B, were exposed to direct sunlight for three minutes. They were then both placed in the dark-box at the same time. They were both found to be non-phosphorescent. A was then continuously agitated and B was left undisturbed except for tests, as above described. A phosphoresced first in 2.5 minutes; B in 3.0 min- utes. After permitting the phosphorescence to develop for a minute or two, A was exposed to direct sunlight for two minutes while B remained in diffuse daylight. A was continually agitated in the dark-box as above described. A phosphoresced first in i minute; B continued to phosphoresce. After some minutes both were exposed to diffuse daylight and then tested as follows: A was agitated in the dark-box, while B remained undisturbed. A first phosphoresced in i minute; B in 2 minutes. The result indicates that exposure to direct sunlight not only prevents phosphorescence, as found in the preceding experiment, but also overcomes a previously acquired power to phosphoresce. Furthermore mechanical stimulation, as before, accelerates the appearance of phosphorescence. Experiment 3. ’It was observed that Mnemiopsis was some- times phosphorescent and sometimes not so after standing for a time in the diffuse daylight of the laboratory. The object of this experiment was to test the power of diffuse daylight, of the inten- sity then prevailing in the laboratory, to inhibit or permit phos- phorescence, as well as to test further the influence of mechanical stimulation. The ctenophores used had been exposed to diffuse daylight. A was agitated in the dark-box, but B, in the same box, was undisturbed except for tests. Both A and B were thien again exposed to diffuse daylight. A was then put in the dark- box and agitated; B was undisturbed except for tests. A phos- phoresced first in 1.7 minutes; B in 2.5 minutes. The results show that diffuse daylight can check phosphores- cence and, as before, mechanical stimulation can accelerate its appearance. Experiment p. In this experiment ctenophores in the dark-hox were continuously agitated with a glass rod to determine wheth< r Phosphorrscciice in (Pcnophorcs. I I I the phosphorescent condition could he removed by excessive mechanical agitation. Reduction of intensity had frequently been observed after long continued agitation. 2.22 p. m. Strong phosphorescence. 2.42 p. m. Phosphorescence appears only in slight gleams, but these persist upon stimulation 'with the glass rod. The result indicates that sufficiently long-continued agitation reduces the intensity of phosphorescence, but does not entirely inhibit it. Experiment The object of this experiment 'was to determine whether the rate at which the ability to phosphoresce is acquired, varies with the intensity of the light. Lots A and B each with six ctenophores, were exposed to direct sunlight for five minutes. The temperature of the sea-water before the exposure was 21^.5 C.; after it, 22^.5 C. Then A was kept in the dark-box until phosphorescent, being tested at intervals (/. ^., not continuously agitated). During the same time B was exposed to diffuse day- light and at intervals it was placed in the dark-box for a momen- tary test. B did not phosphoresce during the whole experiment (19.5 minutes). A phosphoresced first after three minutes in the dark-box, and though kept in diffuse daylight, it retained its phosphorescence over five minutes, after which it lost its phos- phorescence so long as it remained in the light. The result indicates that the ability to phosphoresce is acquired more quickly in darkness than in diffuse daylight and also that phosphorescence has a proportionate relation, in a negative sense, to the intensity of the light. Experiment 6 . Preceding experiments have shown that: (i) darkness is at least one necessary condition for phosphorescence; (2) darkness alone does not result in phosphorescence; and (3) mechanical agitation can caii u'rth and accelerate this phenom- enon in the dark. This compai son suggested the question. Can agitation alone produce phosphorescence ^ To make this deter- mination a lot of ctenophores were poured repeatedly from one dish to another in diffuse daylight and were tested at intervals in the dark-box. The agitation including the tests was continued for a period of ten minutes. No phosphorescence whatever could be detected. The inability of agitation to produce this phenom- enon was frequently observed. I 12 A rnos JV. Peters. This result shows that a non-phosphorescent ctenophore is not made phosphorescent by mechanical agitation alone. Further- more, comparison of all preceding experiments shows that dark- ness accompanied by mechanical stimulation is at least one com- bination of conditions which is able to produce phosphorescence, but its two factors acting singly cannot produce this result. Other stimuli capable of eliciting phosphorescence may, of course, exist. 2. T emperature. Experiment /. This experiment was made to determine the effects of physiological extremes of temperature. It was per- formed in a dark room. A pailful of fresh ctenophores standing there at a temperature of 21^.5 C. emitted, when jarred, enough light to illuminate the room to a considerable degree. From this supply four animals (lot A) were removed to the ice bath and four others (lot B) to the warm-water bath. The respective cooling and warming of the two lots was done simultaneously. The ice bath consisted simply of a basin containing broken ice, in which the vessel containing lot A was partly immersed. Neither ice nor fresh water (from melting ice) came into contact with the animals. They were gradually cooled in their original sea-water. The other lot of animals (B) were warmed in sea-water by placing the vessel containing them over sufficiently warmed water. The tests for phosphorescence were made at intervals by stroking the ctenophores as usual with a glass rod. The temperatures were taken with the bulb of the thermometer in contact with the surface of the animal. Since the phosphorescent parts, the paddle plates, are superficial, the temperatures given apply to these parts. The interior of the jelly might have been at a different temperature. Under these conditions the following record was obtained: Lot A at 2i°.5 C. was strongly phosphorescent; seven minutes later at 12°. 5 C. no phosphorescence could be observed. A was then removed to the warm-water bath whereupon the animals became, after some time, phosphorescent. Hence the previous cessation of phosphorescence was not due to death. Lot B at 21°. 5 C. was also strongly phosphorescent; five min- utes later at 37° C. no phosphorescence was observable. PJjos phorcsccncc in (Ucnophores. i 13 Lot 13 was then removed to the ice bath whereupon the animal became, after some time, phosphorescent. Hence the previous cessation of phosphorescence was not due to death. Experiment 2 . The aim and methods of this experiment were the same as in Experiment i. Lot A at 21^.5 C. was strongly phosphorescent; after 6.5 min- utes cooling it was much diminished, and after 13.5 minutes (9° C.) there was no phosphorescence. Lot A was then placed on the warm water-bath and in 13 minutes became again phos- phorescent. Lot B at 21^.5 C. was strongly phosphorescent; after seven minutes warming the phosphorescence was much diminished, and after ten minutes (38° C.) there was none. At this temperature the animals had completely disintegrated. Experiment The aim and methods of this experiment were the same as in Experiments i and 2. Lot A, strongly phosphorescent at 21°. 5 C., was cooled in ten minutes to 9^.5 C. and became non-phosphorescent. Lot B, strongly phosphorescent at 21^.5 C., was cooled in 12.5 minutes to 1 1^.5 C. and became non-phosphorescent. Another series of experiments was made to determine the effects of variations of a few degrees only from the normal. Such varia- tions, of from one to four degrees above and below the normal (2i°.5 C.), showed, in all the trials but one, a diminution of phos- phorescence as compared with a control. In other words, phos- phorescence in the dark-box appeared sooner in the animals at normal temperature than at any other temperature. It would not have been surprising to find an optimum point slightly differ- ent from the normal temperature. The experiments made upon this subject are not regarded as conclusive. The general result of this work upon temperature may be stated»as follows: The phenomenon of phosphorescence in the ctenophores here investigated occurred during a range of temperature extending from about 9° C. to 37° C., with an optimum at or near 2I°.5 C., which was the temperature of their native sea-water. The inten- sity of phosphorescence diminishes as physiological extremes of temperature are approached. Amos JV. Peters. 114 IV. DISCUSSION OF RESULTS. The preceding experiments demonstrate that the power of phosphorescence is located in the mature animal solely in the region of the paddle plates. I am not aware of direct evidence for a more precise localization than that just given. Allman (’62, pp. 518-519) and Chun (’80, p. 195) attributed this phenom- enon in Beroe to the germinal cells lying in the walls of the gastro- vascular tubes. The supposed fatty, phosphorescent substance of Panceri according to Chun (’80, p. 195) does not exist. Phosphorescence was observed by A. Agassiz (’74, p. 371) in embryos. The experiments described in this paper also show that this property belongs to protoplasm that has but little organic differ- entiation, viz: that of the earlier stages of segmentation. When we inquire what service in the economy of the animal is rendered in the process of phosphorescence we find it difficult to give a satisfactory reply. I have never been able to obtain phosphor- escence in mature ctenophores without the motor activity of the paddle plates, but not every movement of these is accompanied by phosphorescence. Darkness and mechanical agitation are the two selective stimuli whose joint presence results in phosphores- cence. This important fact, taken in connection with the localiza- tion of the reaction, the acceleration of its appearance by mechan- ical agitation, and its complete inhibition by extremes of tempera- ture, lead to a probable conclusion regarding its nature. The phosphorescence of Mnemiopsis is a metabolic reaction which is dependent upon the formation of a substance in darkness, the katabolism of which takes place upon mechanical stimulation and becomes observable as the energy of light. The amount of substance so accumulated may be exhausted by continued mechan- ical stimulation in darkness or may be consumed as produced. When the animal is brought into the light the substance is no longer produced or, if so, it undergoes katabolic transformation rapidly, or the energy is given out in some other form than light. That the phosphorescent substance cannot accumulate in the light is shown by the fact that ctenophores removed from bright daylight or sunlight to darkness are not immediately phosphores- cent. This is the case whether they have been previously agitated or have remained undisturbed. PhosphojTscrnce ni (Ucnophorcs. “5 SUMMARY. 1. riie dead matter originating from ctenophores is not phosphorescent, /. c., only living ctenophores or parts of them phosphoresce. 2. Phosphorescence appears along the rows of paddle plates and no phosphorescence was obtained from jelly free from paddle plates. 3. The smallest piece from which phosphorescence was obtained consisted of four connected paddle plates. 4. Movement of the paddle plates is not always accompanied by phosphorescence. 5. No phosphorescence was obtained from the excised auricles having cilia but no paddle plates. 6. The sense-organ is not phosphorescent. 7. Phosphorescence does not depend upon correlation of the part with the sense organ. The sensory-motor circuits for phos- phorescence are local in character. 8. No phosphorescence could be obtained from the eggs of Mnemiopsis before segmentation. 9. The early cleavage stages (without cilia) are phosphores- cent. 10. Gastrulae (ciliated) are phosphorescent, as are also all stages in which paddle plates are present. 11. The phosphorescence of embryos is easily exhausted. 12. The deposition of eggs can be retarded by light. 13. Direct sunlight prevents the appearance of phosphores- cence, but in darkness, the power to phosphoresce upon stimula- tion, is acquired. 14. Direct sunlight inhibits a previously acquired power to phosphoresce. Diffuse daylight of sufficient intensity has the same effect. 15. Phosphorescence has a proportionate relation, in a nega- tive sense, to the intensity of light. 16. Mechanical stimulation accelerates the appearance of phosphorescence in darkness. 17. Non-phosphorescent ctenophores do not become phos- phorescent by mechanical agitation alone. 18. Long-continued mechanical stimulation reduces the inten- sity of phosphorescence but does not easily inhibit the phenomenon entirely. A 7710 s fV. Peters. 1 16 19. Darkness accompanied by mechanical stimulation is at least one combination of conditions which produces phosphores- cence, but these two factors acting singly cannot produce this result. 20. The phenomenon of phosphorescence was observed at temperatures ranging from about (f C. to 37° C., with an optimum at or near 2i°.5 C., the temperature of the sea-water. 21. The intensity of phosphorescence diminishes as physiologi- • cal extremes of temperature are approached. 22. The phosphorescence of Mnemiopsis is probably a meta- bolic reaction which is dependent upon the formation of a sub- stance in darkness the katabolism of which takes place upon mechanical stimulation and becomes evident to observation as the energy of light. BIBLIOGRAPHY. Agassiz, A., ’74. — Embryology of the Ctenophorae. Mem. Amer. Acad. Arts and Sci., vol. X, pt. 2, no. 3, pp. 357-398, 5 pi. Allman, G. J., ’62. — Note on the Phosphorescence of Beroe. Proceed. Roy. Soc. Edinburgh, vol. iv, no. 57, pp. 518-519. 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