Kinesis in Euplotes vannus-Ethological and Electrophysiological Characteristics of Chemosensory Behavior

ABSTRACT. Equally dispersed Euplotes vannus cells accumulate inside a drop of supernatant of a bacteria suspension that is surrounded by a reference solution. In the drop, frequencies of stops and backward jerks are tenfold increased. The sequences of directional changes and translocations prevent cells from leaving the chemostimulant region, as if they were trapped. This behavior is quickly induced after casual arrival in the drop and not by chemotactic influence over a larger distance. With intracellular recordings, we have found a K⁺ conductance decrease in chemically stimulated cells that prolongs the duration of spontaneously occurring depolarizations to 600-1,700 ms by delaying repolarization. The freely fluctuating membrane potential shifts to more depolarized levels, although the total potential range is expanded in the positive and negative direction by 5.5 and 3.8 mV, respectively. Chemosensory behavior is explained and discussed with respect to these electrophysiological events.     

Circadian rhythm of the locomotor activity in Drosophila melanogaster and its mutants 'sine oculis' and 'small optic lobes'

ABSTRACT. The locomotor activity patterns of wildtype Drosophila melanogaster and the mutants so (sine oculis) and sol (small optic lobes) were investigated. In all strains the proportions showing circadian rhythmicity, arrhythmicity and more complex patterns which could not be thus classified were similar. The occurrence of abnormal activity patterns is thus not a property of the mutation as previously claimed (Mack & Engelmann, 1981). In flies with a distinct circadian rhythmicity, the period lengths (τ) varied between strains, τ for wildtype Italy and the mutant so was longer than for wildtype Berlin and the mutant sol. As different τ's have been reported by others, τ does not seem to be closely determined for Drosophila melanogaster. Many flies exhibited two rhythms simultaneously, one with τ shorter and one with τ longer than 24 h, apparently implying two-oscillator control of the locomotor activity. The eyeless so mutants were entrained by LD cycles, so the compound eyes are not necessary, and so must possess the relevant photoreceptor(s) elsewhere. This may therefore also be true for the wildtype. Histology of the so adults revealed no correlation between the degree of reduction in the medulla and the occurrence of abnormal activity patterns. Since the only structures common to the medulla of so and sol are known to be large tangential cells, it is concluded that either they are of importance for the rhythmic system, or the oscillator(s) controlling locomotor activity is (are) not located in the medulla.     

The Hydraulic Principle

SYNOPSIS. AS theory rules method, the methodological proceduresapplied to morphological explanation have to be derived fromthe law-like properties of the objects under investigation.The explanation of organismic constructions has to be basedon the hydraulic principle which describes organisms as systemscomposed of fluid contained within flexiblemembranes. This insightestablishes a supra-molecular causal principle which, in itsgenerality for morphological explanation, parallels the biochemicalprinciples of molecular biology on the molecular level. Everyform and architectural arrangement has to be conceived as theresult of the form-enforcing influence of mechanical elementsthat operatewithin an integrated mechanically coherent system.An adequate explanation of morphological configuration has toelaborate the organization of the constructional whole and explainits properties as the result of a gradual transformation processthat is constrained by internal mechanical principles. The theoriesdeveloped by such a procedure are open to criticism and canbe tested and corroborated by reference to experiments conductedby nature.     

Studies on the laboratory mating habits of the mosquito Culex pipiens

The variation in copulatory activity in three strains of Culex pipiens is investigated and the results are discussed in relation to genetic control of mosquito populations.     

Photoautotrophic Growth and Photosynthesis in Cell Suspension Cultures of Chenopodium rubrum

A method is described for growing cell suspension cultures of Chenopodium rubrum photoautotrophically for prolonged periods of time. By using a two-tier culture vessel the growth medium with the cells was separated from the CO₂ reservoir. Definite CO₂ concentrations were established by a K₂CO₃/KHCO₃ buffer. Photoautotrophic growth in C. rubrum cell suspension cultures was correlated with the CO₂ level. At 0.5% CO₂ the cell cultures contained 68 μg chlorophyll/g fresh weight and showed an increase in fresh weight of about 80% in 18 days. At 1% CO₂ an increase in fresh weight of 165% in 18 days was observed. The chlorophyll content rose up to 84 μg/g fresh weight. The photoautotrophic growth was also greatly influenced by the 2,4-D content of the medium. Cell growth was enhanced by lowering the auxin concentration. Best growth was attained (210% increase in fresh weight) at 10^?8M 2,4-D. The photosynthetic activity of the cells was measured by the light dependent ¹⁴CO₂ incorporation. At 0.5% CO₂ the cell suspensions assimilated about 100 μmol CO₂/mg chlorophyll × h. In the presence of 1% CO₂ the light driven assimilation was raised up to 185 μmol CO₂/mg chlorophyll × h. In both cases, the dark incorporation of CO₂ was merely 1.8% of the values obtained in light.     

Three Variable Arenopontia Species (Crustacea, Copepoda) from Panamá

Three species of the genus Arenopontia (Cylindropsyllidae) from the Pacific and Atlantic coast of Panamá are presented. Two of them are A. trisetosa Mielke and A. peteruxi Mielke, both of which were described for the first time from the Galápagos Islands. The third species is tentatively identified as A. gussoae Cottarelli previously reported from an interstitial habitat in Cuba.