摘要:

The behaviour of embryos of the lizardLacerta viviparahas been studied in cultured eggs, removed from the mother. Spontaneous movements begin at a time when the embryo is still unresponsive to touch, and about two days before the appearance of reflex responses. The earliest movements consist of lateral flexion which gradually gives place to dorsiventral flexion. Embryonic movements are not necessarily related to contractions of the amnion. The activity of the embryo, as measured by the number of times movements were initiated and the amount of time spent in activity during a half hour period, rises to a plateau and then decreases sharply as the time of hatching approaches. Activity of the tail is prominent, particularly at times when other movements occur in rapid succession. Serpentine movements were not observed in embryos younger than stage 39; some prematurely born animals showed such activity in response to contact with the substratum. During embryonic life any part of the animal may move individually or in combination with any other part, such combined movements being unco‐ordinated. In these respects the spontaneous motility of the lizard embryo closely resembles that of the chick. Statistical analysis of the embryonic movements provides evidence of rhythmic activity within the developing central nervous syste

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04057.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

The African fruit bat,Eidolon helvumKerr, is known to occur only south of the Sahara where its distribution is localized. At 0°20′ N, this bat exhibits seasonal and synchronized breeding the rhythm of which appears to correspond with the two rainfall peaks typical of Uganda. Quite unexpectedly and unprecedently, this bat exhibits delayed implantation lasting about three months. Evidence for this phenomenon comes from the histological examination of the adult female genital tracts which indicate that mating occurs only in April‐June, but implanted embryos are only in evidence in October‐November. The male sexual cycle corresponds to such a rhythm and shows a maximum testicular weight at the mating time. Births take place in February‐March thus giving a gestation period of about four months. Only one young is born at a time and births occur just before the onset of the higher of the two rainfall peaks, presumably creating favourable conditions for the maximum survival of the young bats whe

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04058.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Triassic dicynodonts hitherto described from the Manda Formation of East Africa have been ascribed to the generaKannemeyeriaandDicynonodon.A full description of the skeleton of one species, previously calledD. njalilus, is given for the first time and a new genusTetragoniasis proposed for it. This is based on the shape of the skull in dorsal view and the structure of the palate and intertemporal bar.Tetragoniasis considered to be intermediate in character between the South African Lower Triassic genusLystrosaurusand the well‐knownCynognathus‐zonegenusKannemeyeria.Two kinds of skull are known in this new genus and it is thought they are male and female. It is concluded, from a functional study of the skeleton, thatLystrosauruscould have supplied the ancestor to the later Triassic dicynodonts. The age and correlations of the Manda Formation is discussed and it is concluded that at least part of it is contemporaneous with theCynognathus‐zone.The closest relative ofTetragonias njalilusis the Chinese dicynodontShansiodon wangi

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04059.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Linear measurements were made of the asymmetry of the skull which is characteristic of odontocete whales. Of the living genera (exceptPhyseter, Tasmacetus, Stenella, FeresaandLissodelphis)at least one specimen was measured; 317 skulls in all. One species,Stenodelphis blainvillei, proved symmetrical. All other species had leftward deviation of the nasal prominence. No specimen showed inverse asymmetry.When, for species or families, regressions were formed of the asymmetry measure on skull length the slopes formed a sequence such thatKogia>monodontids>delphinoids (exceptOrcinus)>ziphiids>Orcinus.In some species of delphinoid, in the delphinoids as a group, and more strongly inMonodon, the proportion of asymmetry to skull length increased with increasing size. In the ziphiids, as a family, asymmetry increased roughly linearly with bodily size.Orcinus orcaproved an anomalous delphinoid in having little asymmetry for its size. The asymmetry of the skull ofMonodon monocerosis independent of the possession of a tusk.It is suggested that the leftward deviation of the dorsal aspect of the skull acts to conserve the symmetry of the body surface by countering an opposite asymmetry of the upper breathing passages, an asymmetry which is primary but whose function is unknown.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04060.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Ten species of Phryganeidae are found in the U.K. They also occur in continental Europe and descriptions are available. Certain British larvae show distinct differences and a reassessment of some taxonomic characters is necessary. The immature stages ofAgrypnetes crassicornisare described for the first time from Britain and the fourPhryganeaspecies can now be separated. Eight species have been reared through their complete life‐cycle but the larvae and pupae ofAgrypnia pictaandOligotricha clathrata are, still unknown in Britain. Keys are provide

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04061.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

The segmental musculature ofNereis diversicolorO. F. Müller is described. The musculature ofNereis irrorata(Malmgren),Nereis fucata(Savigny) andNeanthes virens(Sars) is essentially similar but comparison withPerinereis cultrifera(Grube) shows that, at least as far as the oblique muscles are concerned, the segmental musculature of all members of the Nereidae is not identical. A comparison is made with the musculature ofNephthys hombergi(Audouin&Milne Edwards). Swimming inNereisandNephthysis achieved by waves of lateral undulation passing from tail to head with associated parapodial deflection. The promotor and remotor muscles of the parapodium are the ventral parapodial obliques inserting at the parapodial base on anterior and posterior faces. This point of insertion is the hinge line of the parapodium. The dorsal parapodial muscles ofNephthysare more complex than inNereis, apparently associated with the divergent parapodial rami of the former.In slow creeping, intrinsic muscles of the parapodium ofNereisraise it from the substratum and direct it forward, drawing in the neuropodium. Acicular muscles are responsible for its backward extension. The extended notopodium is a firm base for further protraction of the neuropodium. These muscles inNephthysare modified for burrowing; the parapodia help to stabilize the body during proboscis eversion. Acicular muscles extend the parapodial rami dorsolaterally and ventrolaterally to grip the sides of the burrow. Intrinsic muscles withdraw the notopodial and neuropodial tips.The septum ofN. diversicoloris not reduced in the typical body segment and its muscle fibres penetrate the dorsal longitudinal muscle to insert into the circular muscle layer. The pseudoseptum ofNephthysis probably homologous with that ofGlyceraandPhyllodoceand correlated with possession of a long, eversible proboscis.The complexity of oblique muscles inNereisthrows doubt on their alleged polyneuronal innervation. Muscular division of labour in slow and fast parapodial movements is proposed as an alternative to innervation by fast and slow fibres

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1967.tb04062.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY