摘要:

Summary1. The cephalic sutures are defined; their distribution and interrelationships discussed. Few facts are available concerning the evolutionary movements of these, but various theoretical deductions have been made.2. Opinion on the supposed function of these sutures is summarised and it is concluded that the sutures probably did not exist solely for the purpose of ecdysis.3. Consideration is given to the historical aspect of trilobite classification into three orders where the ordinal character is the course taken by some of the cephalic sutures. This classification has been adversely criticised; attention is called to the fallacy of assuming that the chosen cephalic sutures were:(a) relics of primary segmentation,(b) homologous in all groups,(c) in themselves alone of phylogenetic significance.4. Three orders have been erected in turn to accommodate, according to their founders, the most primitive trilobites; none contains a single family in common with another of the orders. Pompeckj's and Swinnerton's objections to Beecher's order Hypoparia are upheld, as are Warburg's and Rud. Richter's objections to Swinnerton's order Protoparia.5. The order Mesonacida (as defined by Poulsen) has a unique position; Poulsen regarded it as the most primitive group of known trilobites; Raw, as the most specialised group at least as far as the cephalic “segmental” spines and sutural evolution is concerned. Disagreement is expressed with this opinion of Raw's, essentially because of a more probable interpretation of the particular segmental origin of one series of spines homologised by Raw, and because there are doubts whether the remaining two spine pairs are necessarily of metameric (segmental) origin.6. Though absolute proof is as yet lacking, Swinnerton and Poulsen are thought to have justifiably stated that the absence of true facial sutures in Mesonacidae is primary; some of the supposed primitive features of the family (or order using Poulsen's restricted sense) are discussed.7. The bearing of recent ontogenetic work on the relationship of Proparia and Opisthoparia suggests that the proparian condition may be regarded as arrested development, and therefore previous failure to recognise this has resulted in the establishment of a group here held to be polyphyletic.8. A satisfactory classification of the group might be evolved, as sufficient reliable knowledge accumulates, by combining allied families into superfamilies. Two attempts at this form of classification are discussed and summarised; these however are based on the primary ordinal value of the supposed (adult) static condition of part of one of the cephalic sutures, and can only be regarded as provisio

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00913.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00914.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SummaryOur knowledge of physiological effects of pressure is as yet too incomplete to permit of generalizations, and we are still very much in the dark regarding the mechanism of pressure action. Any influence of hydrostatic pressure must be secondary to a decrease in volume. In non‐living systems this results in important changes in physical and chemical properties and gives a basis for the explanation of the changes produced in living material. Such factors as the velocity of chemical reaction and the viscosity of fluids are, in general, increased quite out of proportion to the volume change. High pressures bring about an irreversible polymerization of many substances, including proteins. The same order of pressure inactivates most enzyme solutions, bacterial toxins, antibodies, viruses, and other biological agents. The simpler forms of life, such as bacteria and yeast cells, are only slightly less resistant, but all are killed by sufficiently high pressure. On higher forms relatively low pressures cause death, especially when long continued.There are many known instances where small pressures cause a stimulation of physiological processes, and this may prove to be a general phenomenon occurring at pressures below those resulting in depression. In the case of muscle contracting under pressure there is a marked augmentation in the response, and the application of pressure may, independently of any other form of stimulus, result in the prolonged liberation of energy. Provided that the pressure increase is not too extreme, all the changes observed are reversed with decompression.The action of pressure on physiological mechanisms has a special interest because it is a fundamental one on molecular relationships extending throughout the cell structure. Furthermore, it is an agent which can be supplied and removed with great rapidity and as such provides a unique tool for the study of physiological problem

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00915.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00916.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SummaryThis review gives a survey of endemic organisms of the fresh‐water fauna of the circumpolar regions, which have geologically, but not ecologically, separate habitats. A number of examples has been selected which indicate that various animals occur in approximately the same geographical distribution areas as Irmscher established for his plants, although the insufficiency of our knowledge of large regions (e.g.Western and Northern Australia, New Guinea, the west of the Argentine Republic) does not allow of the zoological maps being so complete as the botanical. The similarity of the animal and plant results, however, may perhaps support Wegener's theor

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00917.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00918.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

Summary1. In 1922 it was discovered that a supernumerary transplanted limb in amphibia invariably duplicates the movements of the normal limb in whose nerve plexus it shares. This phenomenon, called “homologous response”, has been demonstrated to be an expression of the more fundamental fact that, in every reflex and spontaneous action, multiple muscles of the same name (synonymous muscles), innervated from the same functional district and the same side of the spinal cord, contract simultaneously and with approximately equal intensities, regardless of their anatomical position, the details of origin and distribution of their nerve supply, and the functional effects of their contractions with regard to the body as a whole. Homologous response of synonymous muscles, observed under such a variety of different conditions as enumerated in Section II (1), has led to the realization that the linkage between the nervous centers and the non‐nervous periphery is based upon mutual relations discriminative for each peripheral organ and much more specific than had previously been suspected. Further experimental analysis of this relationship has led to the following conclusions.2. The specific relations between muscles and centers are not secondarily established by adjustments of the “conditioning” or “learning” type; for, the principal features of the latter, modifiability and adaptive functional value, are absent in the phenomenon of homologous response. In fact, the phenomenon is not even dependent upon the presence of sensory control at all, since it is likewise obtained from limbs with purely motor innervation (III (I)).3. Nor is the specific relation between muscles and centers the result of morphological selectivity in the formation of peripheral nerve connections. Abundant evidence is on hand showing not only that in general no affinity whatever exists between a given nerve fiber and a particular muscle, but more specifically, that such an assumption can be decisively ruled out for the experimental cases exhibiting homologous response. Many new facts have been added in substantiation of this point and are discussed in Section III (2).4. Other explanations being excluded, the specific relation between centers and muscles must be regarded as due to a primary physiological relationship, resembling in principle the specific linkage found in resonance‐like mechanisms. Every muscle is constitutionally (presumably biochemically) different from every other non‐homologous muscle, and to deal with this diversity the centers are endowed with a capacity to produce a corresponding variety of forms or modes of motor impulses, each one exclusively appropriate to a single muscle. Thus, the activation of a muscle becomes a matter of dual activities: release of discriminative emissions from the centers, and the selective reception of these by the periphery.5. Experiments involving the transplantation of single supernumerary muscles in adult toads (IV (1)a) have indicated that the peripheral muscle‐specific selection does not actually occur in the muscle fiber itself but in some part of the peripheral nervous system acquiring its muscle‐specific selectivity through a specifying (“modulating”) effect extending from the muscle. It is assumed that motor neurones subjected to these peripheral influences are gradually rendered specific to such an extent that they will no longer admit from the centers motor impulses other than those appropriate for the particular muscle at their peripheral ends. A study of the reappearance of motility in denervated and re‐innervated limbs in the toad has revealed that the specification of a nerve by its muscle is a slow process. Specification is, at least up to a certain age, reversible, the connection of a nerve with a new muscle resulting in corresponding respecification. Thus, the specific diversity of the muscles is projected into the motor nerves, and E. Hering's postulate of the diversity (“Ungleichartigkeit”) of nerves becomes, after all, a fact.6. Concerning the spinal centers, the conclusion has been reached that their functioning cannot be satisfactorily envisaged in terms of switch‐board or other geometrical schemes (IV (2)). We have been forced to concede to the limb center, for instance, the property to produce, release, and circularize within certain intracentral limits, a variety of specific effects matching the existing variety of individual limb muscles. To judge from experimental evidence, the release of impulses specific for limb muscles is confined to the limb level of the spinal cord.7. It has not yet been possible to offer any suggestion as to the presumable nature of the described selective affinity between central impulse and peripheral nerve fiber. But reasons have been advanced which, it would seem, allow us to reject the idea that specific frequencies or specific chronaxie rel

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00919.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00920.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY