摘要:

SUMMARY1The morphology of the female conifer cones has long been a matter of dispute. In 1900 an account of the theories put forward so far was given by Worsdell. After a brief characterization of the situation at that time, the present article deals with the later history of the subject.2At the turn of the century there were rivalling concepts of the nature of the so‐called ovuliferous scale in the conifers: (a) the Excrescence or Ligular theory of Sachs‐Eichler, (b) the general Brachyblast theory of Braun, Caspary, čelakovský and others, (c) van Tieghem's modification of the Brachyblast theory, and (d) the Foliolar theory of Delpino‐Penzig.3In the subsequent three decades the discussion proceeded on the same or similar lines. The Excrescence theory retained a strong position until the end of the nineteen‐twenties, but, as before, some morphologists professed the general Brachyblast theory. Herzfeld and Wettstein considered that the axillary conifer strobilus had one or more reduced carpels (megasporophylls) which were used up in the formation of terminal ovules, as well as an ‘ovuliferous scale’ consisting of secondary outgrowths from the strobilar axis. In Goebeľs opinion these outgrowths were instead produced by the megasporophylls. Doubts were expressed of the unity of the true conifer group, but Eames showed that the apparently widely different female cones of the Pinaceae and Araucariaceae are homologous, and that the Araucariaceae, Taxodiaceae and Podocarpaceae exhibit complete transitions by fusion and reduction from types with distinctly compound strobilar units–each with an ‘ovuliferous scale’ in the axil of a bract–to others of the most simple form. In contradistinction to the true conifers, the genusTaxushas no compound strobilus, and its ovule is a direct continuation of the axis of the fertile short shoot (Dupler).4In the first half of the period after 1930 opinions differed as much as ever, although the general Brachyblast theory now prevailed over the Excrescence theory and other concepts. Chadefaud believed the ‘ovuliferous scale’ and the bract to represent between them a carpel derived from a prototype analogous to the pinnate megasporophyll ofCycas. Hirmer interpreted the ‘ovuliferous scale’ and the bract as formed by a serial splitting of one single member. Lanfer supported Goebeľs views of the terminal position of the conifer ovules on reduced megasporophylls, and of the nature of the ‘ovuliferous scale’. In Hagerup's opinion the female cones of most true conifers are compound and have a short secondary axis developed axillary to each bract. This axis was supposed to carry two transversal prophylls, fertile (megasporangial) or sterile, and a varying number of sterile leaves; and the megasporophyll, with a megasporangium on its upper side, to constitute the integument of the ovule, and be homologous to a lycopod sporophyll.5Florin (1938‐45) found that the Palaeozoic cordaites and conifers furnished the principal clue to the interpretation of the true conifer cones of Mesozoic and more recent age. Primarily, the fertile seed‐scale complex in the axil of each bract was a radially symmetrical short shoot (strobilus) with several sterile scales and one to a few uniovulate megasporophylls; the ovules were terminal in position. The later types of cones have arisen by the reduction and transformation of this primitive organization, which in the majority of cases has differentiated the strobilus into a proximal fertile part facing the cone axis and a distal sterile part (‘ovuliferous scale’), while its anterior sector facing the bract became totally suppressed. Exceptionally, no ‘ovuliferous scale’ at all was developed, and the strobilus became wholly fertile. The ovular integument is a continuation of the megasporophyll, and appears to arise out of two transversal primordia at its apex. The taxads differ from the true conifers by their simple strobili being placed axillary on reduced vegetative shoots. Their ovules are seated terminally on the strobilar axis itself; megasporophylls are accordingly absent. The living and extinct genera which have previously as a rule been considered coniferous represent therefore two separate subdivisions of the gymnosperms–the true conifers, and the taxads.6Earlier concepts of the morphology of the female cones of the conifers, and of the nature of the integument

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01515.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

RESUMEAprès avoir montré par quelques exemples ľimportance de ľintervention des facteurs internes dans le déterminisme ?une migration, nous exposons pourquoi il nous a paru logique ?étudier en premier lieu, parmi ces facteurs internes, le système neuro‐endocrinien.Un cas particulier–dont nous justifions le choix–est envisageé: celui de la migration ?avalaison du jeune Saumon et des modifications du fonctionnement hypophyso‐thyroïdien la précédant et ľaccompagnant.Il apparaît, ?aprés quelques données encore fragmentaires, que certaines de ces modifications doivent être retrouvées chez ?autres espèces de poissons migrateurs au même stade de la migration.La comparaison ?espèces sédentaires et migratrices suggère ľhypothèse que, chez celles‐ci, le cycle ?activité neuro‐endocrinienne présente des fluctuations plus accusées: Les migrations se manifesteraient à des moments où ces fluctuations entraînent certains hyperfonctionnements ou disfonctionnements neuro‐endo‐criniens mettant en rupture ?équilibre ľorganisme et le milieu, ou sensibilisant cet organisme aux variations des facteurs météorologiques. Nous signalons ?ailleurs que, si nous insistons sur les facteurs internes, trop longtemps méconnus, nous ne sous‐estimons nullement le rôle joué par les facteurs externes dans le déclanchement ?une migration.Le mécanisme hypophyso‐thyroïdien mis en évidence dans le déterminisme de cette migration ?avalaison semble bien se retrouver dans les migrations de certains Oiseaux. Il apparaît done qu'il existe, comme nous le supposions au début de cet exposé, certains facteurs physiologiques du determinisme des migrations communs à des groupes zoologiques fort éloignés.Une brève incursion dans le domaine des Invertébrés montre que, là aussi, le rôle des glandes endocrines dans le déterminisme du comportement migratoire peut être favorablement envisageé.Nous établissons un rapprochement entre les mécanismes physiologiques entraînant les migrations et ceux déterminant ľhibernation. Ces deux comporte‐ments sont le fait ?espèces chez lesquelles les activités cycliques neuro‐endo‐criniennes présentent des fluctuations particulièrement accentuées.Cette caractéristique physiologique est enfin envisageée du point de vue évolutif. Est‐elle primitive, ou au contraire ľaboutissement ?une longue évolution? La question ne peut évidemment etre tranchée, mais elle est ici discutee, et nous apportions quelques arguments en faveur de la seconde hypothèse.SUMMARYHaving shown in several cases the part played by internal factors in the causation of migration, reasons are given for studying primarily the neuro‐endocrine system.A particular instance is selected, namely the downstream migration of young salmon, with the preceding and accompanying modification in the functioning of thyroid and hypophysis.From evidence that is still fragmentary it appears that some of these modifications must also occur in other species of migratory fish at the same stage of migration.A comparison of sedentary with migratory species suggests the hypothesis that in the latter the neuro‐endocrine cycle undergoes more considerable fluctuations. Migrations seem to occur at times when these fluctuations involve neuro‐endocrine hyperfunction or disfunction which upsets the equilibrium between organism and environment, or renders the organism sensitive to meteorological changes. It must be emphasized, however, that while the importance is stressed of internal factors, which have been too long neglected, the part played by external factors in initiating migration is by no means overlooked.The hypophyso‐thyroid mechanism found in the causation of downstream migration seems also to intervene in the migration of birds. It thus appears that there are certain physiological factors in migration which are common to distantly related zoological groups.A study of certain invertebrates shows that here too endocrines are concerned in migration.A parallel is drawn between the physiological mechanisms of migration and those bringing about hibernation. These two types of behaviour are found in animals in which cyclical neuro‐endocrine activities exhibit particularly marked fluctuations.This physiological phenomenon is also considered from an evolutionary point of view. Is it primitive, or, on the contrary, is it the result of long evolution? This question

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SUMMARY1Conodonts are minute, tooth‐like fossils, which exhibit considerable variation in form. Two main types of structure are recognizable, laminated and fibrous. Lamellar conodonts occur in sedimentary rocks from Ordovician to Triassic, while fibrous conodonts appear to be confined to the Ordovician.2Conodonts have been classified as isolated specimens, upon which a binomial system of classification has been erected. This classification does not, however, represent a true zoological classification, since recent work has shown that a number of ‘form‐genera’ appear to have been present in an individual conodont‐bearing animal. This has formed the basis for a zoological classification, which now exists alongside the earlier ‘form‐classification’.3The fibrous conodonts are frequently attached to basal ‘bone‐like’ material. They are apparently confined to the Ordovician, and this suggests that they may represent a distinct group from the lamellar conodonts.4The main variations in form in the lamellar conodonts are described.5The basal cavity of the lamellar conodonts is variable in form. Keels are developed on the aboral surfaces of a number of types, and a few lamellar conodonts are attached to bone‐like material.6Their microstructure indicates that conodonts were formed by accretion around a basal cavity. The presence of radial canals, extending from the basal cavity to the surface of the units, has been detected.7Conodonts are composed of calcium phosphate which has the structure of the apatite series. Analysis shows their composition to be essentially similar to that of the ‘bone‐like’ material to which they are sometimes attached, ridged, bone‐like, fragmentary plates, found associated with the conodonts and a typical Devonian fish‐plate fragment. There appears to be no difference in composition between the fibrous and the lamellar conodonts.8Specimens are recorded in which broken parts of conodonts appear to have been regenerated. The significance of this is discussed.9Palaeontological studies indicate that the conodont‐bearing animals were adapted to a wide variety of shallow‐water, marine environments.10Natural conodont assemblages appear to indicate that conodonts are paired, generally in an antero‐posteriorly elongated arrangement. A single assemblage may contain 14–22 component conodonts, representing 3–5 different ‘form‐genera’.11Conodonts are extinct, having existed from Ordovician to Triassic times. Their geological history is discussed and compared with the histories of other animal groups.12The denticulated jawArcheognathusmay not necessarily represent a group of fibrous conodonts. It is, however, similar to these, and its form tends to support the theory that fibrous conodonts represent a distinct group of animals from those which bore the lamellar conodonts.13The structures on a specimen ofCoelacanthus lepturusdescribed by Demanet do not appear to represent conodonts.14The arrangement, form, number, chemical composition and faunal associations of conodonts do not appear to favour the theories of their crustacean or molluscan origin.15The suggestion of the skeletal function of conodonts does not appear to be favoured by their general form, their assemblage occurrences or the form of their basal cavity.16The evidence for the suggestion of the annelid affinities of the conodonts is discussed. The significance of the chemical composition of the conodonts is considered.17The chemical composition, size and general form of conodonts, and the arrangement of conodont assemblages, appear to contradict the theory that they functioned as copulatory structures in worms.18The reasons for regarding the conodonts as being parts of fish are discussed. The two most important are the chemical composition and the basal attachment of conodonts, but neither of these appears to offer conclusive evidence of the origin of conodonts from fishes. It is suggested that, if the vertebrate origin of conodonts is accepted, they may represent some group of vertebrates, other than fishes, now extinct, and apart from the conodonts, entirely unknown.19It is suggested that the general lack of wear, form, size and assemblage arrangement of conodonts tend to support a theory of their annelid affinities. The main problem appears to be whether the internal secretion of calcium phosphate must be regarded as an indication of vertebrate, rather than invertebrate, origin. The answer to this problem largely determines whether the conodonts are considered as representing vertebrates or worm‐like creatures. It is suggested that the present state of knowledge does not justify a final conclusion as to the affinities of the conodonts, although they appear to represent an extinct group of either worm‐like creatures or primitive vertebrates.It is a pleasure to acknowledge the assistance given by Mr Adrian P. Rhodes in preparing Figs. 1 and 3, Mr Roy Philips for his section on the composition of conodonts, Prof. Harold Scott, of the University of Illinois, for a number of helpful discussions on this subject, Prof. James Cullison, of Florida State University, for supplying information onArcheognathus, Prof. J. B. Cragg and Dr John Phillipson for reading the manuscript, Dr George Kohnstam for translating a paper, Mr G. O'Neill and Mrs J. Harker for assistance in the preparation of the illustrations, and the secretarial staff of the Geology Department of the Durham Colleges for

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SUMMARYAn account is given of the isolation of the outer segments of retinal rods, their internal structure as revealed by the electron microscope, and their chemical composition.The relationship between action spectra (e.g. the scotopic luminosity curve) and absorption spectra is discussed. Provided certain conditions are satisfied, the chemist is able to compare the absorption spectra of pigments isolated from the retina with action spectra which have been recorded for the same type of retina by the physiologist. Thus the absorption spectrum ofrhodopsincorresponds to the scotopic luminosity curve. If there was general agreement on a theory of colour vision, this would give valuable information concerning the number of photosensitive pigments to be expected.At present the only photosensitive pigments whose existence is unequivocal are rhodopsin (found in mammals, birds, reptiles, Amphibia, most fish and the squid), porphyropsin (found in some fish and Amphibia) and iodopsin (found so far only in the fowl). Recent claims to have extracted other pigments are discussed.The extraction and examination of rhodopsin is described. Until recently the various products obtained from rhodopsin by the action of light were characterized by their absoprtion spectra only. These consisted ofretinene, indicator yellow, lumirhodopsin, meta‐rhodopsinandiso‐rhodopsin.The retina has an enzyme, believed to be identical with alcohol dehydrogenase, which catalyses the interconversion of vitamin A andretinenein the presence of coenzyme 1.It has been found possible to effect the regeneration of rhodopsinin vitro. Wald and his co‐workers have shown that a system containing retinene (or vitamin A, coenzyme i and alcohol dehydrogenase) and the specific protein of rhodopsin, ‘opsin’, will synthesize rhodopsin. However, these workers found that synthetic vitamin A or retinene was not effective, but could be made so by exposure to light. Collins and his co‐workers have obtained regenerationin vitrousing synthetic vitamin A or retinene; their systems appear to be nearly complete. They have also shown that pyridoxal phosphate augments the amount of regeneration, although no explanation can be given of this result. The rhodopsin system is outlined in a diagram and table.In the next section an account is given of the results of chemical work aimed at identifying the pigments known only by their absorption spectra. The amounts of these pigments are too small to be isolated and indirect methods have to be used. Retinene has now been identified as vitamin A aldehyde. Indicator yellow has been shown not to be an artifact (as suggested by some workers), and to be a Schiffs base of retinene (anN‐substituted retinene imine). However, the structure of the acid form of indicator yellow is still unknown. Because of their possible connection with visual pigments, a brief account is given of vitamin A amine and methylamine. Certain other reactions of retinene are described (e.g. the reaction with sulphydryl groups) in order to assist the discussion of the nature of rhodopsin itself.The significance of the fact that vitamin A, retinene and retinene methylimine react with antimony trichloride, sulphuric acid and phosphoric acid to give compounds which have absorption spectra resembling the action spectra obtained by physiologists in various retinas, is discussed.The outstanding problems are: (1) the structure of acid indicator yellow, (2) the structure of active‐vitamin A and active‐retinene, (3) the role of pyridoxal phosphate, and (4) the role of sulphydryl groups. Possible alternative explanations are presented, and the evidence for and against discussed.I am greatly indebted to Prof. R. A. Morton, F.R.S., for his many helpful crit

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY