摘要:

SUMMARY1The more important contributions to the literature of animal communities on the sea bottom are summarized.2It is concluded that while there has been much disagreement about the constitution of the communities, the chief criticism has been directed against the view that they are units bound together by biological factors. There is little evidence for this idea. However, most workers agree that communities exist and that there is a correlation between their distribution and that of certain physical factors. Therefore any system of classification should be based on the external conditions.3The factors affecting the distribution of communities are discussed. The significant factors are probably temperature, salinity, and the nature of the bottom deposit.4A scheme of classification applying to the communities of the littoral system is suggested, and an attempt is made to define the range of physical conditions within which each exists. Only the Atlantic boreal region is sufficiently well investigated for the classification to be applied in detail. The communities are described as shallow when the animals composing them are eurythermal and euryhaline within wide limits, offshore when they are eurythermal and euryhaline within narrower limits, and deep when they are stenothermal and stenohaline. Each group is subdivided according to the type of bottom on which the communities occur. There is more or less intergrading between neighbouring communities, both vertically and horizontally.5The more important species occurring in each community are listed and the probable place in the classification of the communities previously described is shown.6The reasons for the existence of animal communities on the sea bottom are discussed. The morphology and mode of life of certain species seem to be important in restricting them to certain grades of deposit, and while analysis of feeding methods does not at present indicate that the latter are of paramount importance in this respect, it is possible that more detailed studies on individual species will prove them to be so.7The quantitative investigations into the fauna of the sea bottom are discussed, and it is concluded that there is little probability of valuable results arising from evaluations at the present time. On the other hand, much useful information may be expected from further studies of the differences in production apparent on different deposits and between different areas, and of the changes in numbers that take place from time to time among the population of a single area.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb01587.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

SUMMARY1Thoracic duct lymphocytes are for the most part newly formed cells; there is only minor circulation of lymphocytes between blood and lymph.2Quantitative studies of thoracic duct lymphocyte production show that, in the cat and rabbit, the number of lymphocytes daily entering the blood via the thoracic duct is sufficient to replace those already in the blood 3‐0‐5‐0 times daily.3Occasionally the blood lymphocytes rise during an experiment in which thoracic duct lymph is being collected. This may mean that in these cases a very considerable number of lymphocytes enters the blood from the lymphoid tissues directly.4Mitotic counts both in sections and in isolated nuclei indicate that lymphocyte formation proceeds most actively in the thymus, and measurements of the nucleic acid turn‐over of lymphoid tissues confirm this.5There is no direct correlation between the total mass of the lymphoid tissues and the level of the blood lymphocytes.6Extirpation of 90% of the lymphoid tissues is usually followed by a transient fall in the level of the blood lymphocytes, and sometimes results in the new formation of lymphoid tissue in liver or lungs. Individual lymph nodes which have been removed do not regenerate. Lymphoid tissue seems to be essential to the body.7Lymphocytes can disappear rapidly from the blood even in the absence of stomach and intestines.8During the first 5 days after removing about 40% of the bone marrow, the blood lymphocytes rise to nearly three times their pre‐operative level.9The subcutaneous injection of egg albumin produces a local accumulation of lymphocytes which in the course of 6 hr. becomes transformed into macrophages.10Tissue cultures of thoracic duct lymphocytes have yielded conflicting results concerning the developmental potentialities of the lymphocyte.11The peculiar nature of lymphocyte movement has been used in an attempt to establish the transformation of lymphocytes into macrophages.12Observation of lymphocytes in transparent chambers in rabbit's ears has shown that they can remain alive for as long as 26 days, though they were never observed to undergo transformation into other cells.13Chemical and spectrographic studies indicate that small lymphocytes have a very low growth rate.14There is a close relationship between the suprarenal cortex and the lymphoid tissues, upon which some of the cortical hormones exert a depressant effect. The adrenotropic hormone of the pituitary exerts a similar action upon lymphoid tissue by stimulating the secretion of the suprarenal cortex.15The precise effect of cortical hormones upon lymphocytes is still not clear; some of the degenerative changes which have been described can be observed also in normal lymphoid tissue. Cortical hormones have no action upon lymphocytesin vitro.16After subcutaneous injection of antigen, antibodies appear in progressively increasing amounts in the regional lymph nodes and in their efferent lymph, reaching a maximum after 6 days. At the same time the lymph nodes undergo hyperplasia with increase in the number of lymphocytes in their efferent lymph.17Tissues and exudates rich in macrophages have a low antibody content.18It has been suggested that suprarenal cortical extract is a potent stimulus to antibody formation, but evidence has also been adduced to the contrary.19The plasma cell may play a major part in antibody formation, though not in the formation of plasma proteins apart from antibody.20The study of the precise cells concerned in antibody formation has revived the controversy concerning the origin of the plasma cell, whether from a lymphocyte precursor or from a specific plasmoblast.21Lymphocytes constitute about 10% of the nucleated cells of normal adult human marrow, though in childhood they may be considerably more numerous.22The absolute count of lymphocytes in rabbit bone marrow was estimated at 61,000 per cu.mm., and in the guinea‐pig 165,000 per cu.mm.23The lymphocyte content of bone marrow is subject to marked variation; this may in part reflect difficulties in cell identification.24Lymphoid nodules are found in adult human red marrow in one case out of three. They do not show the usual mitotic activity characteristic of lymphoid nodules, and are probably focal accumulations of haematogenous lymphocytes.25Viable lymphocytes, marked with acriflavine and injected into the blood, were subsequently found in the bone marrow.26Lymphocytes are found in considerable numbers in the mucous membrane and submucous tissues of the alimentary canal. Experiments to determine whether or not these lymphocytes are excreted into the lumen of the alimentary canal are unsatisfactory.27No quantitative data are available on the number of lymphocytes present in the connective tissues

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb01588.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb01589.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

SUMMARY1The closed tracheal system of the aquatic larvae of insects, together with the typical tracheal gill, can only function if the tracheal tubes themselves have sufficient resistance to compression.2The work of Ege showed conclusively that the ‘air stores’ of many aquatic insects can, if they are in communication with the spiracles, function as gills for a limited time. Such bubbles will, however, since they have no resistance to compression, gradually dissolve in the water unless there is opportunity for regular renewal at the surface. The significance of the concept of invasion coefficient is considered in relation to gas‐bubble respiration.3The term plastron is restricted to a ‘gas store’ communicating with the tracheal system and usually in the form of a thin film of constant and negligible volume and large surface area, retained in position by a system of hydrofuge hairs or scales in such a manner that it is not subject to the ‘Ege effect’ under the normal conditions of its environment, and is therefore not liable to loss by diffusion. Provided there is adequate oxygen in solution in the medium, such a plastron can enable the insect to remain below indefinitely, obtaining all the oxygen it requires from the surrounding water.4The structure and biology ofAphelocheirusas a representative plastron insect is described. The plastron hair‐pile appears to be so perfect that an additional pressure of 4–5 atm. is required before the insect is in danger of losing its plastron and becoming wet. The spiracular adaptations which secure communication between the plastron and the tracheal system are described.5The theory of plastron respiration as established by a study ofAphelocheirusis outlined. It is shown that inAphelocheirusit is fully efficient as a respiratory structure and that this method of respiration has here nearly, if not quite, attained theoretical perfection. The resistance of the plastron hair‐pile to wetting is also discussed, and it is shown that this insect appears to have attained a very nearly perfect compromise between the conflicting requirements of a large area of gas‐water interface for diffusion and a minute scale hair‐pile for efficient resistance to water penetration.6The development of the plastron hair‐pile in the individual and the first appearance of gas on its surface are described.7A survey of plastron respiration in the Coleoptera is given. There are here three main groups in which the method has been elaborated, and while probably none of them presents as efficient an equipment for the purpose asAphelocheirusthere are several which can be regarded as having reached virtual perfection for the particular environments in which they live. It is shown that the plastron insects can be divided conveniently into three groups on the basis of the scale and arrangement of the hair‐pile and the consequent efficiency of the resistance to wetting. A number of the Coleoptera carry, over and above the plastron, a thicker gas layer, the macro‐plastron, held either by longer hairs or by means of a ‘fluffing out’ of the plastron hairs. Such a macroplastron is unstable and can only be maintained by the grooming or special renewal activities of the insects. It is subject to the ‘Ege effect’ and thus resembles in respiratory action a gas bubble rather than a plastron. It may, however, constitute an important first line of defence against wetting, and insects which have a macroplastron provide a number of transitional forms between gas‐bubble respiration and true plastron respiration.8The distinction is made between ‘water‐proofing’ and ‘rain‐proofing’. ‘Waterproofing’ implies resistance to water under pressure and this demands a fine‐scale structure of some rigidity under a maximum of solid‐liquid contact. ‘Rain‐proofing’, on the other hand, implies no pressure of water and requires a more rigid structure of larger scale, the hairs being resistant to matting by lateral surface forces. For such rain‐proofing larger hairs are desirable as giving a minimum solid‐liquid contact. It is possible to trace the development of both types of structure among aquatic and semi‐aquatic insects.9Some of the ecological implications of plastron respiration are described.10A number of other instances of water‐resistant hair‐piles and felts are considered in relation to the evolution of plastron respiration. In the Hemiptera there appear to be no other forms approachingAphelocheirusin plastron efficiency. In the Trichoptera and Lepidoptera there are one or two semi‐plastron forms and one moth,Acentropus niveus,which is perhaps a true plastron insect. The parasitic Hymenoptera provide a number of interesting problems in relation to the wetting and water protection of the cuticle. The larva of one aquatic ichneumonidAgriotypusspins a ribbon‐like appendage to the cocoon, which contains air and appears to act as a plastron. The existence of water‐resistant ha

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb01590.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY