NEMATOCYSTS OF THE SEA ANEMONE METRIDIUM

Six types of nematocysts and their nematocytes in tentaclesand acontia of the sea anemone Metridium senile fimbriatum werestudied by electron microscopy. Microbasic b-mastigophores, microbasic amastigophores, and basitrichshave one fundamental feature in common: a straight, complexly-foldedshaft with dense spines pointing apically. An additional resemblancebetween a b-mastigophore and a basitrich is the possession ofa long, narrow, coiled thread bearing spines. An amastigophoreis characterized by a short, looped, unspined thread and a cup-shapedgranular matrix. Atrich and holotrich nematocysts have a coiled, spined tubeof uniform diameter which lies in an evenly granular matrixfilling the entire capsule. The above five nematocysts have three flaps at the apex of thecapsule which open upon discharge, and each nematocyte possessesa flagellum with which is associated one or two centrioles anda striated rootlet. The long rootlet of the b-mastigophorebearingnematocyte passes through a circular band of fibrils surroundingthe neck region of the capsule, and the short rootlet of theatrich lies in a dense fibrous sheath surrounding all but theapex of the capsule. The spirocyst differs from the other nematocysts in having athin, ridged, singlewalled capsule; an inverted tube containingbundles of tubules; an apical disk covered only by a thin layerof granular material and the nematocyst membrane; and the absenceof a flagellum in its nematocyte. Theories of excitation and mechanism of discharge of nematocystsand the function of spirocysts are discussed in the light ofthis and other recent studies of the fine structure of nematocysts.Special attention is drawn to the probable role of the foldsin the walls of shaft and thread in increasing the length ofthe tube upon discharge.     

PURIFICATION AND EFFECT OF THE NEUROTOXIN FROM THE SEA ANEMONE PARASICYONIS ACTINOSTOLOIDES

— Three toxic components were isolated from the sea anemone, Parasicyonis actinostoloides. Among these components a main component had an effect on the neuromuscular transmission of the crayfish. The component was purified and found to be a basic polypeptide having a molecular weight of about 2000. Amplitudes of excitatory and inhibitory poslsynaptic potentials were increased by the toxin. It was found that the quantum content increased markedly in the excitatory synapse. The action of the toxin remained for a long time after the nerve–muscle preparation was thoroughly washed. These results suggest that the toxin has an effect on the presynaptic nerve.     

VARIATION IN CONTRIBUTIONS OF ASEXUAL REPRODUCTION TO THE GENETIC STRUCTURE OF POPULATIONS OF THE SEA ANEMONE METRIDIUM SENILE

Northeastern North American populations of the sea anemone Metridium senile show marked differences in levels of genotypic diversity. Comparisons with expectations generated by computer simulation show that some populations are genotypically as diverse as expected for sexually reproducing populations with free recombination, whereas others are significantly less diverse than expected, despite efforts to avoid collecting clonemates. These reductions in diversity are not attributable to the Wahlund effect; they probably result from extensive clonal reproduction. Reduced genotypic diversity may be produced by low rates of recruitment of planktonic larvae, followed by asexual proliferation. The resulting founder effect may account for previously documented random allele-frequency variation between adjacent populations. It is presently uncertain whether the few genotypes found in some populations are particularly well-adapted to local conditions.     

NERVOUS ORGANIZATION AND THE PROBLEM OF THE SYNAPSE IN ACTINIA EQUINA

The nervous system of Actinia equina was studied by routinehistological methods and by metallic impregnation techniques.Some preliminary results from electron microscopy are included. The organization of the nervous system of this species is morecomplex than that of other anthozoans; it consists of two interconnectednerve plexuses which are developed to differing degrees in variousparts of the body. These are: (1) a superficial (outer) plexuslying in the ectoderm, and (2) a deeper (inner) plexus constitutingthe main nerve net, lying in the mesoderm. The former is composedof bipolar and multipolar nerve cells, and the latter of multipolarcells. Receptor cells in the ectoderm make contact with fibersof the ectodermal plexus. Processes from the mesodermal plexusrun out to the muscle fibers. Connections between the receptor cells and the nerve processesof the superficial plexus and between the processes of the cteeperplexus and the muscle fibers appear to be of the discontinuous(synaptic) type. In the nerve nets themselves, although someconnections resembling synapses have been seen, most of thenerve elements stand in direct connection with one another,so that the system must be regarded as at least partly syncytial.Evidence is given for the growth of the nerve net, in step withthe general growth of the animal, by division of nuclei followedby their movement apart within the syncytium. The distribution of the nerve elements in various parts of thebody, the interconnections between these regions, and the cytologicalcharacteristics of the cells are described. Ways in which excitationcould pass from one part to another are discussed.     

THE KINETICS OF DARK ADAPTATION

1. Data are presented for the dark adaptation of four species of animals. They show that during dark adaptation the reaction time of an animal to light of constant intensity decreases at first rapidly, then slowly, until it reaches a constant minimum. 2. On the assumption that at all stages of adaptation a given response to light involves a constant photochemical effect, it is possible to describe the progress of dark adaptation by the equation of a bimolecular reaction. This supposes, therefore, that dark adaptation represents the accumulation within the sense cells of a photosensitive material formed by the chemical combination of two other substances. 3. The chemical nature of the process is further borne out by the fact that the speed of dark adaptation is affected by the temperature. The velocity constant of the bimolecular process describing dark adaptation bears in Mya a relation to the temperature such that the Arrhenius equation expresses it with considerable exactness when µ = 17,400. 4. A chemical mechanism is suggested which can account not only for the data of dark adaptation here presented, but for many other properties of the photosensory process which have already been investigated in these animals. This assumes the existence of a coupled photochemical reaction of which the secondary, "dark" reaction is catalyzed by the products of the primary photochemical reaction proper. This primary photochemical reaction itself is reversible in that its main products combine to form again the photosensitive material, whose concentration controls the behavior of the system during dark adaptation.     

SOME ASPECTS OF THE STRUCTURE OF THE NERVOUS SYSTEM IN THE ANEMONE CALLIACTIS

In the light of existing work on tbe behavioral physiology ofthis anemone, the structure of parts of the neuroimiscular systemhas been examined in detail. In the sphincter region, the morphologicalbasis for rapid through-conduction and motor innervation isa network of bipolar nerve cells, which is connected to thesimilar retractor nerve-nets of mesenteries. Sphincter musclefibers are arranged at the periphery of tubes, which form ameshwork within the mesogloea. Bipolar nerve cells appear torun in these tubes. Neurites also reach the sphincter from theendodermal nerve-net by penetrating the mesogloea directly.The nerve-net over the circular muscle is richer than in otherparts of the column, but shows similar features. It includessmall multipolar cells of unknown function. Coordination between different parts of the anemone is discussedin terms of possible pathways for the transmission of excitation.For example, bundles of retractor and parietobasilar musclefibers continue from both surfaces of mesenteries into the mesogloeaof the pedal disk, suggesting a possible route for neuritespassing to or from the ectoderm. If confirmed, the existenceof this route could throw light on a number of sequences ofbehavior.     

西南银莲花皂苷的抗肿瘤作用

目的：对西南银莲花中抑制人癌细胞生长的主要活性成分3－O－鼠李糖基（2）[葡萄糖基（4）]阿拉伯糖基－齐墩果酸（皂苷2）等进行动物体内抗癌活性试验研究。方法：用小鼠肉瘤S180实体模型观测腹腔注射和灌服两种给药途径的抑瘤率,结果:ip皂苷2为10mg/kg时抑瘤率为48．9％,po皂苷2为125,200和500mg/kg时抑瘤率分别为32．6％,39．3％和48．1％,但均不同程度地出现动物死亡,结论：不论腹腔注射[还是灌服给药,皂苷2对小鼠肉瘤S180生长均具有一定的抑制作用,但在有效剂量下已表现出一定的毒性。     

THE GENETIC STRUCTURE OF HOST PLANT ADAPTATION IN A SPATIAL PATCHWORK: DEMOGRAPHIC VARIABILITY AMONG RECIPROCALLY TRANSPLANTED PEA APHID CLONES

Populations of insect herbivores that feed on several host plant species may experience different selective forces on each host. When the hosts cooccur in a local area, herbivore populations can provide useful models for the study of evolutionary mechanisms in patchy environments. A first step in such a study involves determination of the genetic structure of host adaptation in the region: how is genetic variation for host use structured within and between subpopulations of herbivores on each host? The structure of genetic variation for host use reveals patterns of local adaptation, probable selective consequences of migration between hosts, and the potential for further evolution. To estimate the population structure of host adaptation in a patchwork, 7–11 pea aphid clones were collected at the beginning of the summer from each of two alfalfa and two red clover fields within a very localized area (about 15–20 km²). Using a reciprocal transplant in the field, replicates of these 35 clones were allowed to develop individually on each of the two crops. A complete life table was made for each replicate. Individual fitness was calculated from the life tables as the expected rate of population increase; longevity, age at first reproduction, and total fecundity were also measured for each clonal replicate. Currently, experimental estimates of genetic variation in complete life tables are virtually nonexistent for natural populations, even for single environments (Charlesworth, 1987); field studies are even less common. Because clones from each of two source crops were tested reciprocally on both hosts, variation in relative genotypic fitness on alfalfa and clover could be partitioned among clones within source crops, between fields of the same crop, and between source crops (alfalfa or red clover), providing a view of population structure. Significant clonal variation in relative performance on alfalfa and red clover was found: clones tended to have higher fitness on the crop from which they had been collected (the “home” crop) than they did on the “away” crop, suggesting local adaptation in response to patchy patterns of selection. Clonal variability within collections from the two crops suggests the potential for changes in the genetic constitution of these aphid populations within established fields as a result of clonal selection during the summer season. Significantly negative genetic correlations across crops were found for fitness and its major components. The possibility that these negative cross-environment correlations could act as evolutionary constraints on adaptation to the patchwork is considered.     

THE DARK ADAPTATION OF THE EYE OF THE HONEY BEE

Bees which are held in a fixed position so that only head movements can be made, respond to a moving stripe system in their visual field by a characteristic motion of the antennae. This reflex can be used to measure the bee''s state of photic adaptation. A curve describing the course of dark adaptation is obtained, which shows that the sensitivity of the light adapted bee''s eye increases rapidly during the first few minutes in darkness, then more slowly until it reaches a maximum level after 25 to 30 minutes. The total increase in sensitivity is about 1000 fold. The adaptive range of the human eye is about 10 times greater than for the bee''s eye. The range covered by the bee''s eye corresponds closely to the adapting range which is covered by the rods of the human eye.     

ON THE PLACE OF PHOTIC ADAPTATION

The progress of photic adaptation of Agriolimax, when studied by the method of compounding phototropic and geotropic vectors, is shown to be uninfluenced by the concurrent gravitational excitation. Direct proof is thus obtained that the adaptation to light, manifest in its steadily decreasing effectiveness as a stimulus during the course of exposure, is not due to any central nervous adjustment simulating "learning," but is due to photochemical changes in the receptors.     

THE NATURE OF FOVEAL DARK ADAPTATION

1. After a discussion of the sources of error involved in the study of dark adaptation, an apparatus and a procedure are described which avoid these errors. The method includes a control of the initial light adaptation, a record of the exact beginning of dark adaptation, and an accurate means of measuring the threshold of the fovea after different intervals in the dark. 2. The results show that dark adaptation of the eye as measured by foveal vision proceeds at a very precipitous rate during the first few seconds, that most of the adaptation takes place during the first 30 seconds, and that the process practically ceases after 10 minutes. These findings explain much of the irregularity of the older data. 3. The changes which correspond to those in the fovea alone are secured by correcting the above results in terms of the movements of the pupil during dark adaptation. 4. On the assumption that the photochemical effect of the light is a linear function of the intensity, it is shown that the dark adaptation of the fovea itself follows the course of a bimolecular reaction. This is interpreted to mean that there are two photolytic products in the fovea; that they are disappearing because they are recombining to form anew the photosensitive substance of the fovea; and that the concentration of these products of photolysis in the sense cell must be increased by a definite fraction in order to produce a visual effect. 5. It is then suggested that the basis of the initial event in foveal light perception is some mechanism that involves a reversible photochemical reaction of which the "dark" reaction is bimolecular. Dark adaptation follows the "dark" reaction; sensory equilibrium is represented by the stationary state; and light adaptation by the shifting of the stationary state to a fresh point of equilibrium toward the "dark" side of the reaction.     

THE ADAPTATION OF ELECTROENCEPHALOGRAPHY TO MEDICINE

Electroencephalography is a valuable aid in diagnosis and prognosis of diseases affecting the brain. It has definite limitations.Abnormal electroencephalograms are either paroxysmal or non-paroxysmal. Both of these changes may be generalized or focal.Epilepsy is primarily associated with paroxysmal activity. Electroencephalography aids in the diagnosis and in determining the severity, course and response to treatment.Non-paroxysmal activity, although less specific in pattern, indicates either generalized or focal pathologic change or some alteration of the normal structure of the brain. Non-paroxysmal activity may give supportive evidence referable to conditions, systemic or intracranial, which disturb the state of consciousness.     

VISUAL ADAPTATION AND CHEMISTRY OF THE RODS

1. The reality of a chemical cycle proposed to describe the rhodopsin system is tested with dark adaptation measurements. 2. The first few minutes of rod dark adaptation are rapid following short, slower following long irradiation. As dark adaptation proceeds, the slow process grows more prominent, and occupies completely the final stages of adaptation. 3. Light adaptation displays similar duality. As the exposure to light of constant intensity lengthens, the visual threshold rises, and independently the speed of dark adaptation decreases. 4. These results conform with predictions from the chemical equations.     

THE PIGMENTS OF THE ZOOXANTHELLAE SYMBIOTIC WITH THE INTERTIDAL ANEMONE,ANEMONIA SULCATA1

The photo synthetic pigments of the zooxanthellae found in the endodermal tissues of Anemonia sulcata have been identified by column chromatography and spectrophotometry analysis. They appear to be identical with those found among free-living species of Dinophyceae as well as the zooxanthellae of Pacific Madreporaria and Tridacnidae, and confirm the taxonomic relationship which tills symbiont has in common with these organisms.     

THE ADAPTATION OF FUNGI TO FUNGICIDES: ADAPTATION TO COPPER AND MERCURY SALTS

The susceptibility of Botrytis cinerea to copper sulphate in liquid media increased when the volume, and therefore the depth, of the medium in culture bottles exceeded certain values; when the volume was 40 ml. the maximum concentration allowing growth was 300 p.p.m.
By growing mycelium in media containing progressively higher concentrations of copper sulphate a strain was produced which grew at a concentration of 750 p.p.m.
In high concentrations of copper sulphate growth always started at the edge of the liquid, and inocula grew only if they were placed in this position.
In germination tests spores from the resistant strain were more resistant to copper sulphate than were spores of the parent strain.
The resistance of mycelium, and to a lesser extent of spores, was retained after growth of the resistant strain for six months in fungicide-free media.
Spore and mycelial inocula grew in much higher concentrations of copper sulphate when nutrient media were solidified with agar.
The strain resistant in liquid media was no more resistant than the parent strain on agar media.
The resistance of the fungus was not increased after growth for long periods on agar containing high concentrations of copper sulphate. The resistance of the strain resistant in liquid media was not lost after growth on agar media for 3 months.
Attempts to produce strains more resistant than the parent to mercuric chloride were unsuccessful.
The results obtained with phenyl-mercuric acetate were essentially similar to those obtained with copper sulphate, but relatively much more resistant strains were produced.