摘要:

Summary1. The study of the microfauna living in the interstitial water in marine or freshwater sand, the so‐called interstitial or mesopsammic fauna, has made important contributions to systematic zoology during the past four decades. Most invertebrate groups are represented, and many of the morphologically aberrant forms of animals discovered in this environment belong to quite new structural types. Among the discoveries are animal groups of high systematic rank, such as the orders Actinulida (Coelenterata), Gnathostomulida (Turbellaria), Mystacocarida (Crustacea) and Acochlidiacea (Mollusca).2. The coastal subsoil water is the environment of a special interstitial brackish‐water fauna, which has been studied intensively along the beaches of Europe. This zone may be regarded as a transitional area between the submerged marine sand and the continental subterranean waters with their phreatic freshwater fauna.3. One ecological factor of prime significance is that of space, which is dependent on the grain size distribution in a sediment, and which determines the upper size limit of organisms in a given interstitial environment. The granulometric characteristics of the sand affect the composition of the microbiocoenoses and their distribution within a beach area.4. Wind, waves and currents cause a continuous rearrangement of the particles in the surface layer of the sand. The interstitial system of the sand is therefore most usually a very dynamic environment with special biological conditions.5. Such physical factors as temperature and salinity vary greatly in many interstitial biotopes, particularly in the tidal zone. This implies that the interstitial organisms are physiologically adapted to endure both the seasonal variation and the often rapid changes that occur in connexion with ebb and flood. The littoral interstitial fauna is therefore eurythermal and euryhaline.6. The vertical distribution of the interstitial fauna in a sandy beach varies with the situation in relation to low‐ and high‐water marks. The vertical and also the horizontal distribution of the microfauna in a beach show a marked variation with the season of the year, which is usually manifested as a migration towards greater depth during the colder part of the year.7. It is in the interstitial fauna that we find the very smallest representatives of most of the invertebrate phyla. Body sizes vary from about 0.5 to a few millimetres, and only thread‐shaped organisms are longer than this. Protozoa and Metozoa in this environment have about the same dimensions. Examples of morphological regression in the interstitial fauna suggest that body lengths of about 0.5–1 mm. may be the low size limit for invertebrates.8. Certain shapes of body dominate in the interstitial fauna. Elongated forms are favoured; vermiformity is common and may occur in groups of animals in which such a body shape is unusual (the coelenterateHalammohydra, the opisthobranchPseudovermisand others). Another type is represented by the broad and flat forms.9. Morphological adaptations to the biological demands of the dynamic environment are found. These consist of (a) different kinds of reinforcement of the body wall, such as cuticular scales or spines (gastrotrichs, solenogastrids) or epidermal spicules (turbellarians, opisthobranchs), which are of importance as mechanical protection; (b) an often marked ability of contraction serves a similar purpose in organisms with thin body walls (ciliates, turbellarians, gastrotrichs and others); (c) adhesive organs are found in most species, and attachment is by adhesive glands or various kinds of gripping organs; (d) static sense organs are common in different groups of animals and the importance of such organs in a dynamic environment is obvious.10. As regards modes of nutrition, the following categories dominate: (a) predators, e.g. coelenterates, turbellarians, nematodes; (b) diatom‐ and epi‐growth feeders, which may be divided into browsers (archiannelids, crustaceans, molluscs), pump‐suckers (some turbellarians, gastrotrichs, nematodes,Psammodrilus), puncture‐suckers (tardigrades) and sand‐lickers (certain amphipods, cumaceans); (c) detritus‐feeders (some gastrotrichs, nematodes and archiannelids); (d) suspension‐feeders (sedentary forms:Monobryoxoon, a brachiopodGwyniaand the interstitial ascidians).11. The production of gametes is usually low; 1–10 ova per female at a time is normal. Adaptations for the maintenance of the populations of low‐producing species are: (a) spermatophores to ensure fertilization, e.g.Protodrilus, Microhedyle; (b) embryonic and larval development in cocoons, fixed to the substratum; (c) larval development with the suppression of a pelagic phase; (d) brood protection, e.g.Otohydra, Neril‐lidae; (e) considerable extension of the period of reproduction.12. The Ciliata are important in the sand microfauna, where they are represented by almost 90 genera. The ciliates of fine‐sand habitats have been found to be the best adapted to interstitial conditions (microporal ciliates).13. Coelenterates are represented by a rather small number of strongly aberrant forms. Among the Hydrozoa the genusHalammohydrais the best known. The genus forms a morphological series with transitions from ovoid to vermiform species, each adapted to definite interstitial environments, The peculiar bipolar genusSphenotrochusrepresents the Madreporaria.14. Of the two orders of gastrotrichs, the Macrodasyoidea, with itsca. 70 species, occurs exclusively in the interstitial fauna; the Chaetonotoidea are also common here, though this particular group has its main distribution in fresh waters. The macro‐dasyoid gastrotrichs are one of the groups characteristic of the sand microfauna, and provide possibilities for us to study different kinds of adaptation to the conditions of the environment.15. The turbellarians comprise a large and varied group found in practically all types of sand biotopes. Those best adapted to the interstitial conditions are the Kaly‐ptorhynchia, and the Otoplanidae family. The order Gnathostomulida is one of the newly discovered aberrant groups. Members of this group are reminiscent of the familiar turbellarians, but differ in important structural features (cuticular pharyngeal jaws, polygonal epidermal epithelium).16. The Nematoda in the sand fauna are rich in species and occur not infrequently in very large numbers. The distribution of the species in different sand biotopes has proved to be dependent on such ecological factors as grain size and supply of food.17. The undoubtedly polyphyletic Archiannelida form one of the more characteristic groups of the interstitial fauna. Sixty or so interstitial species are known, but only few from other biotopes.18. Ostracoda, Mystacocarida, Copepoda and Isopoda are the most important groups of crustaceans in marine sand. Elongated body forms or elongated shell types (Ostracoda) are common in the interstitial species.The order Mystacocarida, discovered in 1943, is known exclusively from the interstitial fauna, mainly in coastal subsoil water. These very small crustaceans, related to the copepods, have played an important role in phylogenetic discussions.19. The best represented of the mollusc groups are the Opisthobranchia, with the order Acochlidiacea, containing ten species in the size range of 0.8–3 mm., and more or less vermiform. Other typical sand microforms are the generaRhodope, PseudovermisandPhilinoglossa.The groups of molluscs in the sand microfauna to which least attention has been paid are the solenogastrids, which are represented in the so‐calledAmphioxus‐sand by species about a millimetre long.20. The remarkableMonobryozoon ambulansis the only bryozoan in this environment. It has a restricted locomotive ability and may be regarded as semi‐sessile.21. The Echinodermata are represented by a few synaptids a couple of millimetres long, e.g.Leptosynapta minuta, which by shape of body, method of locomotion, adhesive ability, static organs, etc., is very well adapted to life in the interstitial environment.22. Recently discovered interstitial Ascidiacea are ree they belong to various families. Some of the interstitial species have a certain locomotive ability, due to muscle activity.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1964.tb00948.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Summary1. The relatively high refractive index of rod and cone outer segments causes them to show wave‐guide properties.2. Rod outer segments have a positive intrinsic birefringence and a negative form birefringence. The former results from oriented lipid molecules, the latter from the disk structure of the outer segment.3. Electron microscopy of outer segments shows that the disks are formed from infoldings of the surface membrane, each disk consisting of two folds adhering together on their outer surfaces. Studies of other cell membranes have suggested that their lipid molecules form a continuous or discontinuous bimolecular leaflet which is sandwiched between protein layers, and this structure probably applies to each of the disk membranes.4. From the lipid content of rod outer segments a rough estimate of the thickness of a continuous lipid layer in each disk membrane can be made. This is only a little smaller than the requirements of a bimolecular leaflet.5. Rhodopsin is a lipoprotein whose lipid content forms a considerable fraction of the total outer‐segment lipid. This and other data suggest that rhodopsin may be a structural component of the disk membrane.6. The initial effect of light on rhodopsin is probably to isomerize II‐cisto all‐transretinene, and various thermal rearrangements follow which eventually cause the detachment of retinene from opsin. The absorption spectrum of rhodopsin is similarin situand in solution, but the absorption spectra of the photoproducts are somewhat different.7. Rhodopsin is strongly dichroic in the rod, indicating that the retinene molecule lies mainly in the plane of the disks.8. Rhabdomeres, the photoreceptor organelles of many higher invertebrates, are formed from close‐packed microvilli. They show a negative birefringence which probably results from the lipid molecules within the microvillar membrane.9. All well‐authenticated rhabdomere visual pigments have a retinene chromophore, and in many features the photochemical processes resemble those of vertebrate rhodopsin. The extraction processes for vertebrate and invertebrate rhodopsins are also similar.10. The question of whether insect rhabdomeres show dichroism is still open, but there is good evidence for dichroism in some cephalopod rhabdomeres. This is probably the physiological basis for the polarized light discrimination shown byoctopus.11. Some possible mechanisms for the transmission of the light stimulus within photoreceptor organelles ar

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1964.tb00949.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryThis article is devoted to photochemical reaction systems other than photosynthesis present in plants which enable normal growth and development to take place. In many higher plants (e.g. dicotyledonous seedlings) at least four different photochemical reaction systems are effective:(1) the photochemical system related to photosynthesis,(2) the photochemical system related to phototropism,(3) the phytochrome system,(4) the so‐called ‘high energy reaction of photomorphogenesis’.(1) is beyond the scope of this article which is limited to those photoreactive systems in plants which directly control growth and development.The term ‘phytochrome’ is used today to signify the pigment system of photo‐morphogenesis which has been most thoroughly investigated and which is apparently common to all potentially green plants. From the algae, mosses and ferns to the monocotyledons this pigment system is of fundamental importance. It is composed of a complex chromoprotein present in the cytoplasm, which can be isolated from the cell and brought into watery solution. Phytochrome has two interconvertible forms, phytochrome 660 (P 660) with an absorption maximum in the red at 660 mμand phytochrome 730 (P 730) with an absorption maximum in the far‐red at 730 mμ. The non‐irradiated, dark‐grown plant contains almost entirely P 660 which is stable in the dark. P 660 is converted by exposure to red light into P 730. Conversely P 730 can be reconverted into P 660 by exposure to far‐red light. Even in the dark P 730 slowly changes back into P 660 Temperatures above zero and in the presence of oxygen are necessary. P 730 is the physiologically active form of the phytochrome system. Apparently it is an enzyme. As soon as P 730 is available, reactions occur which cannot proceed without it and which finally lead to the observable photo‐morphogenic responses.In 1957 it was demonstrated that phytochrome cannot be the only photoreactive system in photomorphogenesis and anthocyanin synthesis, and experimental data made it necessary to suppose that a further photoreactive system plays a part. By contrast with phytochrome this other reaction system can be physiologically demonstrated only by irradiating relatively strongly for a long period of time (therefore called high energy reaction). This reaction system is not reversible. Under natural conditions of radiation it seems to be very important; it is apparently as widely distributed as phytochrome. To study the high energy reaction more closely it has been necessary to separate responses due to it from those due to phytochrome. This has been done by the use of rather complicated irradiation programmes, in situations involving either synergism between phytochrome and the high energy reaction (e.g. with mustard seedling) or antagonism (e.g. movements of the plumular hook in lettuce seedlings). The situation becomes more simple when we investigate photoresponses which are not markedly influenced by phytochrome and are largely under the control of the high energy reaction (e.g. hypocotyl lengthening in lettuce seedlings). The known action spectra of this reaction show peaks of the same order of magnitude in the blue and in the far‐red range of the visible spectrum. The mode of action of the high energy reaction is far from firmly established. One hypothesis is, that the activation of an enzyme (e.g. a metal‐flavoprotein) by visible radiation is the basis of the reaction. This enzyme must be of fundamental importance in metabolism because many different photoresponses are controlled through the high energy reaction.In a typical dicotyledonous seedling elongation of the hypocotyl is controlled by the phytochrome and by the high energy reaction. That is, the control of axis growth can be effectively exerted by long‐wavelength visible light (above 600 mμ). A phototropic curvature, however, can be induced only by the shorter wavelengths of visible radiation, i.e. wavelengths below 500 mμ. There is thus no immediate relation between phototropism and control of stem growth by phytochrome and the high energy reaction.The germination of fern spores and the growth of the gametophytes are strongly influenced by light. In recent years it has been possible to demonstrate that several physiologically distinct photoreactive systems control development and morphogenesis during these stages: (1) the photochemical system concerned with photosynthesis, (2) the phytochrome system (germination, partly morphogenesis, partly phototropism), (3) a photoreactive system dependent on blue light mainly controlling morphogenesis and partly phototropism and germination. In the case ofDryopteris filix‐masnormal morphogenesis, i.e. the rapid formation of two‐ or three‐dimensional prothallia, can only occur under short‐wave visible light (blue light). In darkness and under long‐wave visible light (red light) the gametophytes grow as filaments. The control of morphogenesis by a blue‐light‐dependent photoreactive system is connected with the increase of protein synthesis under the influence of the light and with changes in nuclear volume and chloroplast size. These gametophytes are a clear example of the control of nuclear and cellular properties by an external factor, light.Phototropism and polarotropism of the protonernatal filaments can be induced by blue and by red light. The polarotropic response, i.e. control of the direction of growth by the plane of vibration of the electrical vector of linearly polarized light, must be regarded as a variant of phototropism mediated by an orientation of dichroic photoreceptor molecules with respect to the nearby surface. An action spectrum of polarotropism indicates that both phytochrome and the blue‐light‐dependent pho

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1964.tb00950.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Summary1. Many birds are capable of varying the rate of evaporative heat loss during respiration as a means of temperature regulation.2. Respiratory heat loss becomes increasingly important as air temperatures rise. Above the body temperature of the bird it is the only means of heat loss.3. The rate of respiratory heat loss varies from one species of bird to another. The rate is also dependent on environmental atmospheric humidity.4. The rate of heat loss by respiratory evaporation is dependent on the difference in vapour pressure between that of the respiratory surface and of the inspired air, on the degree of saturation of the expired air, and on the volume of air expired per breath and per unit time.5. There is a constant relation between breathing rate and heat production in the House Sparrow above the upper critical temperature.6. Other things being equal, there is a constant relation between evaporative rate and the vapour pressure difference between the air and the evaporative surface, if one assumes that the vapour pressure of the respiratory surface is equal to that of water at the rectal temperature of the bird.7. When variations due to differences in respiration rate, metabolic rate, atmospheric humidity and body size are excluded, in some species of birds the rate of evaporative heat loss is essentially constant at air temperatures above the upper critical temperature (the upper limit of the thermo‐neutral zone, see p. 114, footnote). In other species the rate of respiratory evaporation increases as air temperatures rise above the upper critical temperature.8. From this evidence and other data in the literature, there appear to be four classes of species: one in which respiratory evaporation as a temperature‐regulating mechanism is unimportant or non‐existent; a second in which respiratory evaporation takes place in the lungs and air sacs and in which, at air temperatures above the upper critical temperature, increased evaporation is achieved only by an increased respiratory rate; a third in which respiratory evaporation takes place in the lungs and air sacs but the evaporative rate can be enhanced without an increase in respiratory rate; and a fourth in which evaporation takes place in the more anterior regions of the respiratory tract such as the trachea or buccal cavity.9. These four groups are interpreted as representing various stages between two extremes of specialization. One extreme is represented by species of cold arid regions in which all or most of the tidal air passes through the lung parenchyma. Respiratory evaporation and hence heat loss is thus minimized. The other extreme is represented by species of hot humid regions in which the major function of ventilation is to provide evaporative heat loss. Respiratory gas exchange is a minor purpose and only a small fraction of the tidal air traverses the lung pas

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1964.tb00951.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY