摘要:

SummaryThe methods employed for the work recorded in subsequent Parts are described. The gaits of the Arthropodaveraappear to have been evolved from those of soft bodied ancestors using a locomotory mechanism such as is seen in Peripatus. Each group has restricted the versatility of its gaits and perfected the type adopted. It is suggested that habits determined the general nature of the gaits employed, and that perfection of the gaits occurred along with the evolution of associated morphological features. Many of the latter are diagnostic features of the larger groups.It is suggested that the evolution of many of the larger groups of the Arthropoda has been determined by differentiation and persistence of habits, and that adaptations to particular environments have been of lesser importance.The arthropodan type of integument and muscle has led to an improvement in leg structure. The majority of terrestrial Arthropoda do not ‘stand up’ on their legs, aa do the vertebrates, but ‘hand down’ from them, and most groups have adopted an advantageous method of stapping which is impossible to the Onychophora.The effects of leg length and leg number on the fields of leg movement are considered in relation to the evolution of body form.The mechanism for changing speed in the Arthropoda differs from that of the Onychophora. Change in pace duration has become a major factor additional to the effects of changes in the gait and in the angle of swing of the leg.A relationship is shown between the shape and number of the trunk segments and the type of gait employed; ‘bottom gear’ gaits requiring short, and often numerous segments, and ‘top gear’ gaits requiring longer and fewer segments.The phase difference between the paired legs, which may be used in the same or in opposite phase, or in some other phase relationship, is shown to be dependent upon the nature of the gait in animals with many legs. The conditions in animals with few legs is considered.Undulations of the body, either lateral or dorso‐ventral, tend to occur at fast speeds and are disadavantageous. Morphological features which minimize or prevent these undulations are:—wide, short segments, alternate sized tergites, diplo‐segments, a small number of long legs borne on consecutive fused segments (t

ISSN:0368-2935    

DOI:10.1111/j.1096-3642.1952.tb01854.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

SUMMARY.1The locomotory mechanisms of the several groups of Chilopoda and of the Pauropoda are described, together with the factors which determine the choice of the gaits and the morphological features which make possible their execution.2The Epimorpha alone show small changes in body length associated with changes in the gait.3The gaits of the epimorphic and anamorphic Chilopoda are fundamentally different, and have evolved from the further development of types of gait seen in Peripatua ‘middle’ and ‘top gears’ respectively (pp. 121 and 158, and Part 1, p. 554).4Comparison of the gaits of the Onychophora, Chilopoda, Pauropoda and Diplopoda indicate that the locomotory mechanism and the structure of the body wall and limbs in the Onychophora are primitive, and not secondary derivations from jointed animals, p. 160.6Morphological characters facilitate the execution of the gaits and render them mutually exclusive. A phase difference between successive legs of>0.5 is shown by the Epimorpha correlated with short legs, and one of<0.5 is obligatory in the Anamorpha in consequence of their long legs. The footprints of all legs on one side of the body occupy common marks at each pace in the Epimorpha, but form forwardly directed ‘sets’ in the Anamorpha. Crossing of successive legs occurs in the recovery stroke in the Anamorpha and to a very small extent in the propulsive stroke of the Epimorpha.6Changes of speed are effected in the Epimorpha mainly by changes in pace duration and in gait, but in the Anamorpha in addition by changes in the angle of swing of the leg.7The gaits of the Geophilomorpha and Scolopendromorpha show the same wide range of prtttérn, approx. (5.0: 5.0) to (7.5: 2.6), at a phase difference between successive legs of 0.6–0.87, and form a series of even practicability. The gaits are elaborated for different purposes in the two groups. The Scolopendromorpha achieve fast speeds for surface running by steeply decreasing the pace duration to<0.04 sec. and the duration of the backstroke to<0.01 sec. The Geophilomorpha, increase the flexibility of the gait, varying the positions of the footholds, for a, burrowing or cryptic habit, and the pace durations do not steeply decrease.8Active burrowing in the Geophilomorpha is dependent upon the body becoming ‘fat’, and not upon the motive force exerted by the legs. A longitudinally contracted animal can increase its length by 66%.9Morphological specializations correlated with burrowing in the Geophilomorpha, are:—(i) shortness of legs, (ii) presence of intercalary sclerites, which are large dorsally and telescope freely, (iii) the staggered position of the dorsal and ventral joints of the body, (iv) the elastic pleural region with isolated sclerites, (v) the powerful longitudinal musculature, and (vi) the tendency to decrease the length of the segments and increase their number.10Morphological specializations correlated with running in the Scolopendro‐morpha are:—(i) the curtailment of the number of body segments, (ii) the longer legs of differential length, and (iii) alternate sized tergites.11The gaits of the Anamorpha show a smaller range of pattern than the Epimorpha, forLithobius(5.5: 4.6) to (6.54: 3.46) at a phase difference between successive legs of 0.16 to 0.154, and forScutigera(5.6: 4.6) to (6.43: 3.57) at a phase difference of 0.16 to 0.135. Great speed is achieved by the reduction of the pace duration to approx. 0.07 sec. and that of the backstroke to approx. 0.02 sec. Lateral undulations are considerably controlled.12The gaits are operated by either thirteen or fourteen pairs of legs, and result in an even mechanical performance, footfalls occurring at approximately equal intervals, the loads on each leg remaining constant.13The gaits of the young stages ofLithobiusare described. The second instar with eight pairs of legs employs only a slow type of gait (5.0: 5.0) at a phase difference of 0.25; a faster gait with an even mechanical performance is not possible until more legs are present.14Morphological features correlated with running in the Anamorpha are:— (i) alternate sized tergites and fusion of tergites as inScutigera, (ii) long legs of differential length, (iii) reduction in number of leg bearing segments to fifteen, and (iv) a tendency to shorten the trunk segments.16The methods of starting up and turning are described.16The main limiting factors to increase of speed are, in the Scolopendromorpha:— (i) sagging of the body between the propulsive legs, and (ii) lack of control of lateral undulations of the body, which results in a waste of energy and a loss of potential speed; and in the Anamorpha:—mainly an inability to quicken the pace still further.17The gaits of all stages ofPauropus gracilisare described. They bear a basio similarity to the epimorphic Chilopoda, but owing to their environment, the animals can effect a simultaneous transfer of the weight from leg to leg.18Morphological features associated with the gaits in the Pauropoda are:— the alternate sized tergites and the length of the segments.19The evolution of the body form of the main groups of Chilopoda is discussed., Support is given for the view that epimorphic development and a moderate number of segments may be primitive, and that anamorphic developments may be secondary. The nature of the locomotion has led to a shortening of the body in the Lithobio‐morpha and Scutigeromorpha and to an elongation of the body in many Geophilomorpha. The Scutigeromorpha represent the most advanced and swiftest, and not th

ISSN:0368-2935    

DOI:10.1111/j.1096-3642.1952.tb01855.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

ISSN:0368-2935    

DOI:10.1111/j.1096-3642.1952.tb01856.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

ISSN:0368-2935    

DOI:10.1111/j.1096-3642.1952.tb01857.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

SUMMARY.1The holotype ofH. vulpiceps, nearly complete and uncrushed, is the best known skull and jaws ofHyracotherium. It is refigured to show the structure more clearly than in previous published illustrations.2The holotype ofH. leporinum, also uncrushed but fragmentary, reveals foramina and other details of the orbital wall. Exact homologies are dubious, in part, but the various possibilities are pointed out. In any case there are significant differences fromEquus.3Teeth of hyracotheres are extraordinarily variable. No two specimens are in really close agreement. This is especially well exemplified by P3, which seems not yet to have been fully brought under a unified field control of the cheek‐tooth series.4Specimens from the London Clay do not suffice to show whether their strong variation was segregated into two or more separate specific populations or was manifested in a series of interbreeding populations, perhaps with some progressive temporal change. The two supposed species,H. leporinumandH. vulpiceps, have not been soundly differentiated or defined, and, apart from the types, no specimen can be confidently placed in one species rather than in the other. The older species,H. cuniculus, from Kyson, is probably distinct but also lacks adequate definition. Specimens from the Blackheath Beds are more like those from the London Clay, but are also impossible to allocate soundly as to specific or subspecific relationships.5There are no constant or surely signifimnt structural differences between British and Amercian early Eocene hyracotheres as now known, and Forstar‐Cooper must be followed in consideringEohippusas a synonym ofHyracotherium. “Eohippus” might well be retained as a vernaculer name forHyracotherium.8British specimens ofHyracotheriumare not, as a group, more primitive than American specimens. Most British specimens are about as advanced as those found in the early Eocene of the United Statea. The perhaps most primitive British specimens are not clearly more primitive than the oldest American forms, and some London Clay specimens seem to compare best with rather advanced, late Wasatchian, America

ISSN:0368-2935    

DOI:10.1111/j.1096-3642.1952.tb01858.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY