Hinz, I., Kraft, P., Mergl, M. & Müller, K. J. 1990 04 15: The problematic Hadimopanella, Kaimenella, Milaculum and Utahphospha identified as sclerites of Palaeoscolecida. Lefhaia, Vol. 23, pp. 217–221. Oslo. ISSN 024–1164.
Hadimopanella Gedik, 1977, Kaimenella Marss, 1988 and Milaculum Müller, 1973 have been established on the basis of isolated elements of unknown origin. Recently, the latter genus has been tentatively related to the Agnatha (van den Boogaard 1988). By contrast, Bendix‐Almgreen & Peel (1988) assigned Hadimopanella to the chordate stock but definitely excluded it from vertebrates. Well‐preserved worm‐like organisms of Palaeoscolecida Conway Morris & Robison. 1986 are known from the Lower Cambrian to the Lower Ordovician. They have their outer surface covered with a pattern of sequin‐like sclerites which evidence the systematic affiliation with the isolated sclerites mentioned above. Based on similar structures on the outer surface, Utahphospha Miiller & Miller, 1976 is considered to belong to the same group. *Early Palaeozoic fossils, Palaeoscolecida, isolated sclerites, phosphatization.
SUMMARY1. Synaptic transmission in the two cutaneus pectoris muscles of frog was compared after prolonged unilateral nerve stem stimulation in vivo via surface electrodes.2. In Mg2+-blocked preparations at 2 Hz stimulation the mean number of quanta released per impulse (m) was significantly lower in the stimulated muscles. On average, m was reduced to 53% (range 31-74%) of the values in control muscles.3. Similarly, in curare-blocked preparations end-plate potential (EPP) amplitudes in the stimulated muscles were reduced to 30-92% (average 63%) of the control values, while no differences in muscle fibre diameter and resting potential were detectable. 4. In most muscles plateau values after tetanic stimulation at 40 Hz for 2 s were also smaller in the stimulated muscles. Compared to the first EPP in the train, however, plateau values were less depressed in stimulated than in unstimulated muscles. Also facilitation, i.e. the amplitude ratio of the largest versus the first EPP was more pronounced in stimulated muscles.5. No effects of stimulation were noticed in four winter frogs, in which transmitter release is depressed due to seasonal factors.6. It is concluded that prolonged nerve stimulation can cause under certain conditions profound depression of transmitter release with changes in facilitation and depression.
The radial contraction-relaxation activity was recorded in Physarum by the infrared technique either at distant sites or along a linear array of 5 or 10 sites, each 2.5 mm distant from each other. There is a tendency in the plasmodium to maintain the same period throughout the whole plasmodium, although the period may change with time. The recording at a single site represents aggregated rhythms, the mode of which is either synchronous, or twinned or of the shoulder type. The last two modes refer to a split rhythm. There is also a tendency toward synchrony at neighbouring sites. However, there is often a gradient of phase along the array of recorded sites. The gradient is pot stable and often shows a reversion. This reversion displays the type 0 resetting; the resetting occurs spontaneously. Usually the resetting takes place only in a part of the oscillating system at a certain site. The local synchronous mode may thus be changed into the twinned or the shoulder mode.
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