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Showing papers in "Biological Reviews in 1974"


Journal ArticleDOI
G. P. Arnold1
TL;DR: Fish have a wide range of responses to currents, extending beyond simple orientation, and the term rheotropism is therefore used as a ‘portmanteau’ word to describe all such reactions.
Abstract: Summary (1) The fluid properties of air and water enable animals to orientate to flow and this behaviour in water is termed rheotaxis. Fish, however, have a wide range of responses to currents, extending beyond simple orientation, and the term rheotropism is therefore used as a ‘portmanteau’ word to describe all such reactions. (2) Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are called optomotor reactions. The lateral line is not involved except in the detection of small localized jets of water. It has not been demonstrated that any fish can detect the current by electrical stimuli, although it is theoretically possible for some to do so. (3) In the basic form of rhotaxis the fish heads upstream and maintains station by stemming the current. Current detection thresholds fall within the range 0.4 to 10 cm/s for tactile stimuli but may be as low as 0.03 cm/s for visual stimuli. (4) Visual responses have been studied by simulating displacement by the current in optomotor apparatus. Fish respond to a rotating black-and-white-striped background by compensatory movements of the head and eyes - optokinetic nystagmus - or by the optomotor reaction, in which the fish swims with the background. (5) Fish show an orthokinesis in optomotor apparatus, their mean swimming speed increasing with the speed of rotation of the background. The precise form of the relationship varies between species and there is also considerable individual variation in performance. Fish accelerate and decelerate relative to the background, fixating on a particular stripe for short periods. (6) Factors limiting the appearance of the optomotor response are contrast, illuminance, acuity, critical flicker fusion frequency and spectral sensitivity. (7) Fish tolerate retinal image movements equivalent to those received when they are carried forwards by the current but not to those received when they are carried backwards. There are ganglion cells in the optic tectum which are sensitive to the direction of movement of targets across the visual field. In the goldfish there are significantly more units sensitive to movements in the temporo-nasal than in the opposite direction. (8) There are close parallels between the behaviour of fish in schools and in an optomotor apparatus. The optomotor response is apparently innate, occurring in newly hatched fry. (9) Physical and chemical factors can modify rheotaxis. Temperature and olfactory stimuli affect both the sign of the taxis and the kinetic component of the behaviour. (10) Thyroid hormones which are involved in the control of migration have been shown to affect the kinetic component of rheotaxis. (11) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams, which show extreme dorsoventral flattening and have specialized adhesive organs. Other fish select areas of low velocity or decrease their buoyancy with increasing current speed. (12) Rheotropic behaviour plays an important role in the distribution of fish within stream systems, in the maintenance of territory and station and in feeding behaviour. Territory, station and spawning sites in salmonids are all selected in relation to water velocity. (13) Water currents are thought to provide either a transport system or directional clues for fish on migration. The fish either does not respond to the current and is carried passively downstream, or it makes an orientated movement, swimming up- or downstream. (14) Eggs and larvae are known to drift passively downstream from their spawning grounds and some adult fish may also drift passively. In the sea both adult and juvenile fish use a form of modulated drift associated with vertical migration. Fish move up into midwater either by direct tidal selection or in relation to the diel cycle of illuminance. In fresh water the downstream migrations of salmonid fry, and smolts under some conditions, occur by modulated drift. (15) There is no evidence that fish migrating in the sea orientate to the current, but in fresh water the upstream migrations of diadromous fish are clearly orientated movements. (16) Water velocity is a major factor for salmonids migrating upstream. For fry it limits the occurrence of upstream migrations and for adults it can also prevent upstream movement. But migrations are often initiated by freshets, and changing water velocity is thought to be the most important factor associated with a freshet. (17) Both environmental and genetic factors affect the direction of migration in relation to the current. In some sockeye salmon fry direction is determined by temperature, but in others the overall direction of movement is genetically determined and environmental factors only modify the behaviour. (18) Rheotropic behaviour has a number of important practical applications in the capture of fish and in guiding them past dams and power stations. (19) The optomotor response plays a basic role in the capture of roundfish by trawls under conditions when the fish can see the gear. Many fish are caught because they become fatigued after a prolonged period of swimming at the same speed as the trawl. (20) Most success in guiding fish away from hazardous areas and bypassing them round dams has been achieved with mechanical barriers which depend on rheotropic reactions of the fish. (21) Louvre screens are very successful in deflecting juvenile salmonids migrating downstream past small dams but are impracticable at large dams. Instead, the turbine intakes are commonly sited at a considerable depth and fish are bypassed by mechanical screens either at the surface of the forebay or into the gatewells immediately upstream of the turbine intakes. (22) With upstream migrants the basic problem is to attract fish to the lower end of the fishways. An adequate ‘attraction velocity’ is an important feature of fishways, which must be sited so that the fish avoid the high velocity discharges from spillways and turbines.

247 citations


Journal ArticleDOI
TL;DR: In this paper, the authors propose a method to solve the problem of the problem: this paper...,.. ].. ).. ]... )...
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238 citations


Journal ArticleDOI
TL;DR: In this article, the authors propose a method to solve the problem of the problem: this article...,.. ].. ).. ]... )...
Abstract: CONTENTS

141 citations


Journal ArticleDOI
TL;DR: These cases of apparently spontaneous parthenogenetic development suggest that the cells of the female germ line have an inherent tendency to divide and differentiate.
Abstract: Summary and Conclusions 1. The eggs of many mammalian species show signs of early parthenogenetic development as they age after ovulation and oocytes may form transplantable terato-carcinomas. These cases of apparently spontaneous parthenogenetic development suggest that the cells of the female germ line have an inherent tendency to divide and differentiate. 2. The ovulated eggs of virgin female mammals may be stimulated to start parthenogenetic development by a wide variety of treatments. Most of these damage the egg so that it does not develop beyond the 4 cell stage. However if the eggs are exposed to electrical activation, hyaluronidase treatment, or temperature shock then in many cases they will develop into blastocysts. 3. These blastocysts may be either haploid or diploid. Haploid blastocysts may be formed either by the egg extruding the nucleus of the second polar body or by the egg dividing in half, so that the female pronucleus is in one cell and the nucleus of the second polar body is in another cell. Diploid blastocysts are formed by the retention of the nucleus of the second polar body within the egg. The way in which the egg develops may be controlled by altering the osmolarity of the culture medium, the age of the egg at the time of activation, or the strain of animal used. 4. The action of the sperm on the egg can be defined by comparing the events of normal fertilization and parthenogenetic activation. Both these stimuli cause the egg to expose binding sites for Concanavalin A to synthesize DNA and to divide. However, the release of cortical granules, which occurs after fertilization, does not appear to be induced by parthenogenetic activation, and it is significant that parthenogenones lack the sperm nucleus and mitochondria. 5. The majority of parthenogenones die soon after implantation. Death at this time occurs with parthenogenones obtained from the activated eggs of both inbred and outbred stocks. Death might be caused by recessive lethal mutations or by extra-genetic effects of the maternal chromosomes. 6. Parthenogenones contain endogenous A-type particles which shows that these bodies are inherited through the female germ line. 7. Parthenogenones may in the future provide both a method for chromosome mapping and a source of haploid cells. At present the use of mammalian parthenogenones in biological research is restricted by the heavy embryonic losses which occur around the time of implantation. This means that the role of the sperm, gene activity and virus expression must be studied during a very limited period. Part of the mortality before implantation is the consequence of the damage which the egg suffers during activation and it should be possible to reduce this loss by improving the techniques for activation. It may also be possible to increase the quantity of cells derived from haploid and diploid mammalian embryos by deriving teratocarcinomas from them.

129 citations


Journal ArticleDOI
TL;DR: The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog.
Abstract: Summary 1. The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog. The heat and cold tolerances of peripheral conduction are probably both increased by cold acclimation in the frog. 2. The properties of compound action potentials are not suitable for temperature acclimation studies, since different neuronal populations in the same nerve have been found to exhibit different temperature characteristics. 3. Single but septate giant nerve fibres of earthworms show compensatory temperature acclimation of the conduction properties, the form of the action potential and of the axonal cable properties, especially below 13–19 °C. 4. The fatty acids and the plasmalogen aldehydes of the phospholipids of the goldfish brain are more unsaturated at lower acclimation temperatures. 5. The Na+-K+ ATPase activity of the earthworm nerve cord shows compensatory acclimation at low temperatures. 6. The spontaneous activity of the central nervous system of insects is altered in a compensatory manner by temperature acclimation. In fish, the cold tolerance of simple and complex reflexes and of conditioning is adaptively altered by temperature acclimation. The role of the central nervous system, especially of the thermoregulatory centre, in the temperature acclimation of homeotherms is established. 7. There are adaptive isoenzymes of acetylcholinesterase in the brain of the rainbow trout. These isoenzymes differ from each other in respect of the temperature dependence of their enzyme-substrate affinity. The synthesis of acetylcholine receptor molecules may also be affected by temperature acclimation. 8. The metabolism of putative synaptic neurotransmitters (5-hydroxytryptamine, adrenaline, noradrenaline) is altered in the frog and mouse brains during the early phases of temperature acclimation. These changes may initiate the physiological processes connected with temperature acclimation. 9. The neuromuscular transmission in the frog shows after acclimation to cold, increased resistance to it and some indications of temperature compensation. 10. Changes in neurosecretion seem to be involved in temperature acclimation both in poikilotherms and homeotherms. The fast axonal transport of proteins shows compensatory acclimation to cold in the frog.

123 citations


Journal ArticleDOI
TL;DR: This review attempts to collate data about the structural and functional dimorphism of mammals exclusive of the genital organs and psychological aspects about males and females in aspects not directly connected with reproduction.
Abstract: 1. Life expectancy and mortality rates from diseases arising in various organs vary with sex because of differential exposure to external hazards and because of essential differences between males and females in aspects not directly connected with reproduction. This review attempts to collate data about the structural and functional dimorphism of mammals exclusive of the genital organs and psychological aspects.

120 citations


Journal ArticleDOI
TL;DR: Evidence is often patchy but suggests a number of generalizations regarding the course and causes of the developmental changes in these tropical ecosystems.
Abstract: Summary 1. The flooding of a lake basin initiates a series of changes leading eventually to a more stable climax situation after some years. Sequential physical and chemical changes in the mud and water and related changes in the animal and plant populations of three types of tropical African lakes are considered. The giant man-made lakes, Kariba and Volta, both several thousand square kilometres in area, provide the bulk of the material for this review. Two other kinds of tropical lake, the annual storage-reservoirs like Jebel Aulia and Sennar in the Sudan, and natural lakes subject to periodic droughts, like Lake Chilwa in Central Africa, are also considered. Evidence is often patchy but suggests a number of generalizations regarding the course and causes of the developmental changes in these tropical ecosystems. 2. On the evidence available, the course of development appears to fall conveniently into two periods based on water level changes, the filling phase and the post-filling phase. The former is characterized by sudden appearances of organisms and explosive growths of animal and plant populations. This unstable behaviour, especially characteristic of tropical lakes, is associated with the destruction of old habitats and the creation of new ones, the increasing area and volume of the new lake environment and the introduction of materials to the system at the advancing shore-line. By the time that filling is complete, the situation has stabilized to a large extent and the ecosystem enters a new phase. 3. This post-filling phase is characterized by the development and exploitation of existing habitats. Examples considered here are: the development of the mud habitat under the influence of processes like sedimentation and beach formation; the development of submerged woodland as a habitat for bottom dwelling animals; the spread of rooted aquatic plants and their effect on the mud; and the role of fluctuation in water-level on the post-filling phase. All four phenomena result in a modification of the substrata originally flooded, in a way that directly effects the associated fauna and flora. Apart from influencing the first three processes, water-level fluctuations also result in an interaction between the aquatic and terrestrial ecosystems which brings about important changes in itself. 4. The relative importance of these two phases varies with the type of lake, filling-phase phenomena obviously dominating in the annual storage reservoirs while post-filling phase characteristics are fully expressed in the large lakes made by man. 5. In contrast to the development of temperate lake ecosystems, succession of species in these tropical examples is not so much interrupted by major annual temperature changes. In addition, both the course of succession and the climax communities achieved are different. This may be largely due to the more rapid decomposition of organic matter in the muds which has two main consequences. In the first place, extraneous organic material brought in to the system during flooding, is rapidly broken down. Early filling stages, therefore, are associated with anoxic conditions and development of conspicuous communities of algae and large aquatic plants. The result is an overlapping of what in temperate systems are two distinct episodes: the early extraneous and later self-contained systems. Secondly, the replacement of chironomids by an oligochaete climax in the mud as seen in temperate lakes does not normally occur, apparently because of the lack of accumulated organic material. The presence in Africa of the may-fly Povilla adusta, on the other hand, provides an extra stage in the colonization of submerged woodland, replacing the earlier chironomid communities.

97 citations


Journal ArticleDOI
TL;DR: In gastropod molluscs, hormones secreted by the cerebral ganglia, glandular ‘dorsal bodies’ and/or optic tentacles are responsible for the control of the development of the reproductive tract, and the activity of the gonads.
Abstract: SUMMARY 1 Neurosecretory phenomena are apparently ubiquitous among Metazoa. 2 In Hydra, neurosecretory products are probably involved in the control of growth and reproduction. 3 Secretory elements in the central nervous system of turbellarians probably promote fission, regeneration and reproduction. 4 The cerebral ganglia of nemertines are the source of a hormone which exercises an inhibitory influence on maturation of the gonads and the development of somatic sexual characteristics. A principle secreted by the ganglia and/or the associated cerebral organs controls weight regulation. A sex hormone controls sexual differentiation. 5 Secretory neurons may influence the production of exsheathing fluid and ecdysis in nematodes. 6 In nereid polychaetes, a single hormone which originates from the cerebral neuroendocrine system apparently promotes segment proliferation and inhibits maturation. However, in certain other polychaetes, contrasting endocrine mechanisms seem to operate. 7 In lumbricid oligochaetes, a hormone secreted by the cerebral ganglion (and possibly by other nervous centres also) promotes gonadal activity and the differentiation of somatic sexual characters. In some species the ganglion exerts an inhibitory influence on the associated processes of ‘diapause’ and posterior regeneration. The cerebral and suboesophageal ganglia are implicated in the control of osmoregulation. Cerebral neurosecretory cells in limicolous oligochaetes may influence regenerative growth and osmoregulation. 8 The cerebral ganglia of leeches secrete a gonadotrophic hormone. 9 In gastropod molluscs, hormones secreted by the cerebral ganglia, glandular ‘dorsal bodies’ and/or optic tentacles are responsible for the control of the development of the reproductive tract, and the activity of the gonads. Contrasting mechanisms are thought to operate in the different gastropod groups and there is conflicting evidence particularly with respect to the endocrine functions of the optic tentacles and the gonads. The ‘bag cells’ of the abdominal ganglion of ApZysiu secrete a hormone which induces egg-laying. Cells in the pleural and parietal ganglia probably control osmoregulation in Lymnaea. 10 The optic glands of cephalopods secrete a gonadotrophic hormone, but sex hormones are apparently absent. The functional significance of the neurovenous tissues (presumptive neurosecretory complexes of unusual character) is obscure in most cases. 11 The radial nerves of starfish are the source of a hormone which induces the production of I-methyl adenine by the follicle cells of the gonad. This second principle stimulates oocyte maturation and the shedding of male and female gametes. 12 The relevance of such information to the development of certain biological concepts and to various aspects of comparative physiology is briefly discussed.

90 citations


Journal ArticleDOI
TL;DR: This review covers the Pleistocene history of British non‐marine Pisces, Amphibia, Reptilia and especially Mammalia, which alone have a good fossil record, and the relationship between faunal history and vegetational history, as determined from fossil pollen and macroscopic plant remains.
Abstract: SUMMARY 1 This review covers the Pleistocene history of British non-marine Pisces, Amphibia, Reptilia and especially Mammalia, which alone have a good fossil record. Aves are also briefly discussed. 2 The fossil material available is often inadequate for purposes of taxonomy and identification. Further problems arise because many groups of Mammalia have undergone rapid evolution during the Pleistocene. 3 In this paper the fossil record is related to the currently accepted stratigraphic table of the British Pleistocene (Shotton & West, 1969). Wherever possible, fossil records have been assigned to pollen assemblage zones. Throughout, emphasis is placed on the relationship between faunal history and vegetational history, as determined from fossil pollen and macroscopic plant remains. 4 Although fossils are relatively scarce in the fluviatile and lacustrine deposits of open sites, compared with the often rich cave assemblages, the stratigraphy of the former is usually much clearer and the sediments commonly contain pollen. It is difficult to correlate cave sequences with those of open sites. 5 It is important to take into account possible bias in a fossil assemblage according to its mode of accumulation, e.g. assemblages from occupation sites may represent only those animals which were hunted by man. 6 Lower Pleistocene vertebrates are rather poorly-known. The majority of fossils are from the marine Crags of East Anglia (Pre-Ludhamian to Pastonian) and a single cave assemblage of this age is known (Dove Holes). Few records can be related to particular stages, but a few finds from Easton Bavents are assigned to Antian and Baventian stages. 7 Early Middle Pleistocene vertebrates are represented mainly by the rich assemblages from the marine and fresh-water Weybourne Crag and Cromer Forest Bed Series (Baventian to Early Anglian) of Norfolk and Suffolk. The East Runton fauna appears to be of pre-Cromerian (?Pastonian) age. A good fauna is known from the type Cromerian deposits at West Runton (zone Cr 11). A few records are available for zone ?Cr III and one for the Early Anglian. The assemblages from other localities appear to represent more than one stage at each site, e.g. the so-called ‘Bacton Forest Bed’ fauna is composite, including both Cromerian and ?Pastonian taxa. Outside East Anglia one open site (Sugworth) and one cave fauna (Westbury) of probable Cromerian age are known. 8 Many of the fossils found in lacustrine and river-terrace deposits of the Middle and Upper Pleistocene glacial-interglacial succession (Anglian to present day) can be assigned to particular stages, zones or even subzones. Cave assemblages rarely predate the Ipswichian. No pre-Devensian records are available for either Scotland or Ireland. The Anglian fauna is very poorly known. The Hoxnian is represented principally by the Clacton (zone Ho IIb) and Swanscombe faunas. The Baker's Hole deposit, the basal gravels of the Summertown-Radley Terrace and the Glutton and Bear Strata in Tornewton Cave have yielded faunas of probable Wolstonian age. The early Ipswichian is poorly represented (Selsey), many fossils are known from zone Ip Iib (e.g. Trafalgar square, Swanton Morley, Aveley), there are a few records from early zone Ip III (Aveley, Swanton Morley) and fairly good faunas from zone Ip III/IV (Histon Road, Stutton). Several open and cave-site faunas resemble those of zones Ip II and Ip III and the assemblages from Ilford, Brundon, etc., appear to date from the end of this interglacial. The Early Devensian is represented by the Wretton fauna and probably by some cave faunas. Middle Devensian faunas are fairly well known (e.g. Upton Warren) and there are a number of records for the Late-Devensian (Ballybetagh, High Furlong, Nazeing). Many cave faunas date from the Middle or Late Devensian. Good faunas are available from the early Flandrian, zone F1 I (e.g. Star Carr). The present-day native fauna (zone F1 111) is also discussed. 9 The main faunal characteristics for each subdivision of the Pleistocene are summarized in the Conclusions. There is a major faunal change between the predominantly Tertiary fauna of the Red Crag Nodule Bed (Probably Pre-Ludhamian and older) and that of the Red Crag (Pre-Ludhamian and Ludhamian). There appears to have been comparatively little change in fauna through the rest of the Lower Pleistocene but the more intense climatic fluctuations of the Middle and Upper Pleistocene were accompanied by rapid faunal change and the appearance of characteristic ‘steppe-tundra’ faunas in the Wolstonian and Devensian cold stages. The Late-Devensian and Flandrian faunas are impoverished in comparison to earlier stages. This may be partly due to the activities of man as well as climatic and vegetational changes. 10 There is usually good agreement between fauna and vegetational conditions when these can be compared, but a few taxa (e.g. Cricetus cricetus, Equus) have clearly changed their ecological requirements during the Pleistocene. Changes of fauna in response to vegetational changes within interglacials are known from the Hoxnian and especially the Ipswichian. The ‘steppe-tundra’ vegetation of cold stages was accompanied by a mixture of animals nowadays extinct or living in either steppe or tundra.

58 citations


Journal ArticleDOI
TL;DR: If some metabolic processes are slower in mammals destined to be large, corresponding trends in age‐related cellular changes which ultimately suppress mitotic activity may cause differences between species in the overall size of muscles and in that of other tissues.
Abstract: Summary 1. Fibres of skeletal muscle in different mammalian species vary more in number and in their rates of growth than in their ultimate breadth, and they grow more slowly in cattle and man than in rats and mice. Cells of large mammalian species probably divide comparatively slowly in pre-natal life but do so for longer, and thus they attain greater numbers than do their counterparts in smaller mammals. Such cells include the precursors of muscle, and common mechanisms may therefore limit rates of growth before and after muscles form. If some metabolic processes are slower in mammals destined to be large, corresponding trends in age-related cellular changes which ultimately suppress mitotic activity may cause differences between species in the overall size of muscles and in that of other tissues. This is probably an oversimplification. 2. It is difficult to decide how far the rate of growth and the final diameters of muscle fibres reflect the number of myoblasts which initially fuse into myotubes and the number of myoblasts which are subsequently incorporated into individual fibres. New nuclei are probably added with age along the length of a fibre, but it is uncertain whether they then synthesize ribosomes which produce contractile protein. It seems likely that fibres elongate to different extents by adding myoblasts terminally. 3. There is some evidence that myofibrils grow throughout the depth of a fibre by adding new myofilaments to their surface, but there is none that is convincing to the effect that myofibrils form de novo at a fibre's periphery. Ribosome-like structures distributed in the sarcoplasm between myofibrils have been described, and their numbers decline in comparison with those of the myofibrils during growth. Thus, fibres possibly attain their maximum breadth when the loss of superficial filaments from myofibrils exceeds the capacity of ribosomes to replace them. The evidence is inconclusive as to whether myofitrillar protein is broken down and replaced at rates which vary within a muscle or between muscles differing in physiological properties. Sarcoplasmic proteins appear to be replaced more rapidly than those in myofibrils. It is also speculated that muscle proteins are synthesized and degraded more slowly in species which take longer to develop. 4. Observations, with the microscope suggest that new ribosomes appear in cells which are becoming myoblasts. Whether the ribosomes subsequently break down is not established. The evidence that I-somes occur in muscle is inconclusive, as is that for the existence of messenger RNA and its selective synthesis when muscle is forming in the embryo. 5. A decline in the synthesis of RNA occurs as myotubes appear and contractile protein begins to accumulate. The significance of this phenomenon is not known, and in more mature muscle some RNA also appears to fluctuate in a fashion which is unrelated to rates of controlling protein synthesis. Such RNA may occur at the periphery of fibres or in satellite cells. In some instances it may be formed by cells of the connective tissue and capillaries. There are indications that the growth of muscle does not require the continued transport of new RNA and ribosomes into the body of a fibre. 6. As regards the existence of polyribosomes in muscle and the activity of muscle ribosomes in zlitro, most relevant phenomena can be explained if the ribosomes are aggregated, inter ah, by newly completed protein and if observed variations in activity are some function of the residual amounts of nascent protein which remain on the ribosomes. The morphological appearance of ribosomes in myoblasts is difficult to reconcile with the notion of ribosomes linked by messenger RNA. There is also some rather inconclusive evidence that the sarcoplasm varies in the effectiveness with which it supports protein synthesis by ribosomes. 7. Muscle fibres differ markedly in the number of mitochondria which they exhibit in histological sections and in the rate at which the homogenized fibres catalyse the processes of aerobic respiration which occur in mitochondria. It is uncertain how far such variation is determined by the properties of myoblasts and myotubes, by the nature of subsequent contractile activity and by dilution of the mitochondria as myofibrillar protein accumulates. In part, the tendency of fibres richest in mitochondria to be comparatively small may reflect the diversion of energy sources and oxidizable precursors of protein into energy-generating pathways. However, such fibres perhaps also possess fewer nuclei and fewer functional ribosomes. 8. Within a given animal, variation between fibres in the activity of sarcoplasmic enzymes becomes most pronounced after the myoblast stage. Assuming that these sarcoplasmic proteins are increasing by dissimilar amounts, genes in different fibres are perhaps varying in activity, but this has not been studied. It may be that the intermittent and increasingly forceful contractions of developing fast-phasic fibres simply cause them to accumulate increased amounts of amino acids in the pool from which protein is synthesized, so that a generalized stimulation of protein synthesis follows. Sarcoplasmic protein should then accumulate more than myofibrillar protein relative to starting quantities. This is a consequence of sarcoplasmic protein turning over faster. However, in addition, one must postulate that sarcoplasmic enzymes vary in stability between fibre types. It also remains to assess whether such differences reflect the presence of different molecular forms of each enzyme and whether the latter possess dissimilarities of amino-acid sequence or of molecular configuration. Similar unsolved problems arise regarding the ATPase activity of myosin in developing muscles and its variation between fibres.

44 citations


Journal ArticleDOI
TL;DR: In this article, the authors propose a method to solve the problem of the problem.II.XII. XII, p. 6.1.1-3.0.
Abstract: XII. XII

Journal ArticleDOI
TL;DR: Four species of locusts are called the main species; other species are Dociostaurus maroccanus of Morocco, Call+tamus italicus of Southern Europe and Western Asia, and Chortoicetes terminifera (the Australian Plague Locust).
Abstract: Since biblical times it has been known that locust swarms cause great damage to grassland, agricultural crops and various other plants such as citrus. These losses are not confined to North Africa, Asia Minor or India, the invasion territories of the Desert Locust (Schistocerca gregaria), for other species of locusts occur elsewhere. The Red Locust (Nomadacris septemfasciata) spreads its invasions mainly from Lake Rukwa in Tanzania to Central and Southern Africa; the Brown Locust (Locustanapardalina) of the Karoo Plateau of South Africa invades a large part of Southern Africa; the Migratory Locust (Locusta migratoria) has various so-called subspecies, e.g. capito in Malagasy, migratorioides in Tropical Africa, gallica in south-western France, migratoria in Middle Asia, the Caucasus and Ukraine, rossica in central European Russia, cinerascens in Mediterranean countries, manilensis in south-eastern Asia and India. The four above-mentioned species may be called the main species of locusts; other species are Dociostaurus maroccanus of Morocco, Call+tamus italicus of Southern Europe and Western Asia, and Chortoicetes terminifera (the Australian Plague Locust). Locusts are polymorphic species of gregarious Acrididae, with a range of morphological and physiological characteristics varying between two extremes, the solitaria and gregaria. Intermediate forms, including the whole range of transitions between the extreme forms, are called transiens. Solitary locusts were originally thought to belong to different species of grasshoppers until Uvarov (1921) formulated the theory of phase transformation of solitary locusts (the solitaria phase) into crowded locusts (the gregaria phase). The original observations were mainly on Locusta migratoria and for this species Plotnikov (1927) was the first to observe the phase change in the laboratory. He, however, thought that the two extreme phases consisted of closely

Journal ArticleDOI
TL;DR: 1. Primitive vertebrates have many characters which do not appear to be immediately represented in any obvious precursor, but these characters are nevertheless represented in many primitive vertebrates.
Abstract: Summary 1. Primitive vertebrates have many characters which do not appear to be immediately represented in any obvious precursor. 2. The hypothesis is put forward that creeping, or bottom-living worms, classifiable as nemertines, attempted to recolonize the water by acquiring buoyancy, by swimming or both. 3. Some of those that succeeded were able to do so by adopting a method of filter-feeding made adequate by the development of gill slits, and then converting the proboscis rudiment into a semi-rigid structure (the notochord) essential for oscillatory swimming movements. These were the precursors of the protochordates and the vertebrates. 4. The acquisition of the ability to swim efficiently depended on the simultaneous development of distance receptors and the co-ordination of the information that they provided with that provided by proprioceptors on the one hand and with the changing motor systems on the other. This entailed the development of a far more extensive nervous system, probably by incorporating into it much more of the dorsal ectoderm, and superimposing a primarily sensori-motor system on to the more vegetative system already present in nemertines. This was achieved by elaboration of the placodal folding of the ectoderm which is characteristic of many nemertine embryos of the present day. In this manner a new central nervous system was combined and integrated with the existing more primitive ‘autonomic’ system and the cephalic ganglia of the nemertines became incorporated in the hypothalamus. 5. The hypothesis suggests likely precursor tissues from which the following vertebrate structures could plausibly have developed: olfactory organ, lateral line system, anterior and posterior pituitary, thyroid, pineal organ, chloride-secreting cells, oxyntic cells, notochord, urinogenital system, liver, and several others. 6. The possible origins of the vertebrate eye, the somitic muscles, and some other fundamental features of the vertebrates are discussed. The evidence is still equivocal. 7. The acquisition of filter-feeding and swimming by nemertine worms would be expected to bring into operation a whole new system for the selection of appropriate genes and thus inaugurate a period of very rapid and probably divergent evolution, made even more rapid by the enormous advantages gained by animals acquiring efficient form-vision together with rapid and well co-ordinated movements. It is thought likely that the rapid evolution of this group of animals, which possessed few features conducive to clear fossil remains, accounts for the apparent break in the continuity of the story of animal evolution which has until now made the origin of the vertebrates such an enigma. 8. It is suggested that studies of the proteins and secretions of the various organs of the nemertines and their comparison with those of the organs of the more primitive vertebrates might lead to the establishment of some important homologies.