Transparency in organisms

Summary The occurrence in animal phyla of species having a relatively transparent body is noted and measurements of the transmittance of medusae made in a spectrophotometer are reported, but the approximate nature of the results obtained with a commercial instrument and the importance of the correct physical design of the measuring apparatus are emphasized. The application to invertebrates of the structural explanation of the predominant transmission of incident light by the vertebrate cornea is discussed and the role of other factors considered. Destructive interference of the scattered rays, sufficient to account for the transparency of the cornea, has been shown not to demand a completely regular arrangement of collagen fibres. The small diameter and regularity of the fibrillar components in the muscles ofSagitta may be adequate to account for their transparency.I am grateful to Dr.D. M. Maurice for the encouragement of this interest, to Dr.E. G. Jordan for electron micrographs ofSagitta and to Mr.G. Ross (Department of Physics, Queen Elizabeth College) for helpful and critical discussion.     

Cornea regeneration in the Pacific giant octopus,Octopus dofleini,and the common octopus,O. vulgaris

Summary Cornea regeneration in a Pacific giant octopus,Octopus dofleini, occurred within 10 days after the injury was observed. Surgical removal of the cornea in 2 common octopi,O. vulgaris experimentally duplicated this cornea regeneration within a 10-day period. It is, therefore, concluded that besides sucking discs, arms, and nerve fibres, octopi can also regenerated corneal tissue.The authors would like to thank U. E. Friese, B. Borowski, P. Burn, J.W. Atz, G.J. Nelson, H. Feinberg, P. Fenimore, C. Roper, M. Nixon, M. Segalla, G. Clark, D.O. Calligaro, J.M. Anderson and R.J. Koestler for assistance and advice. Illustrations were drawn by G.D. This work was supported by the New York Aquarium of the New York Zoological Society, while G.D. was at the New York Aquarium.     

Retention of topical liposomal formulations on the cornea

Summary The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I¹²⁵-labelled phosphatidylethanolamine derivative and were instilled in 10 l drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery, liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea.     

L'activité succino-déhydrogénasique dans le tissu oculaire (étude histo-chimique)

Summary The author has studied, with different tetrazolium techniques (NT, INT, nitro-BT), the succinate dehydrogenase activity in the ocular tissue (cornea, ciliary body, lens, retina).     

Synthesis of sulfated glycosaminoglycans by the three cell types of the rabbit cornea in culture

Summary Rabbit corneal cells were cultivated for 21 days and then exposed to Na₂ ³⁵SO₄, a precursor of sulfated glycosaminoglycans (GAG). All 3 cell types of the cornea, the fibroblasts, the epithelial as well as the endothelial cells, synthesize GAG. The fractionation-patterns of the epithelial and endothelial GAG are almost identical and differ clearly from the one of fibrolastic GAG.Supported by SNSF, grant No. 3.534.71.     

Retention of topical liposomal formulations on the cornea

The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 microliters drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea.     

Amphibious vision in Coryphoblennius galerita L. (Perciformes).

The morphology of the ophthalmic cornea in the blenniid fish Coryphoblennius galerita (Teleostei) shows adaptation to the amphibious life. Amphibious vision is provided by a flattened area within the cornea. Eyes of other, non-amphibious blenniids are compared with those of C. galerita.     

Structural and biochemical aspects of keratan sulphate in the cornea

Keratan sulphate (KS) is the predominant glycosaminoglycan (GAG) in the cornea of the eye, where it exists in proteoglycan (PG) form. KS-PGs have long been thought to play a pivotal role in the establishment and maintenance of the array of regularly-spaced and uniformly-thin collagen fibrils which make up the corneal stroma. This characteristic arrangement of fibrils allows light to pass through the cornea. Indeed, perturbations to the synthesis of KS-PG core proteins in genetically altered mice lead to structural matrix alterations and corneal opacification. Similarly, mutations in enzymes responsible for the sulphation of KS-GAG chains are causative for the inherited human disease, macular corneal dystrophy, which is manifested clinically by progressive corneal cloudiness starting in young adulthood.     

Forecasting for the generation of trading signals in financial markets

In this paper we show that optimal trading results can be achieved if we can forecast a key summary statistic of future prices. Consider the following optimization problem. Let the return r_i (over time i=1, 2, ..., n) for the ith day be given and the investor has to make investment decision d_i on the ith day with d_i=1 representing a ‘long' position and d_i=0 a ‘neutral' position. The investment return is given by r=Σⁿ_i=1r_id_i−cΣⁿ⁺¹_i=1∣d_i−d_i−1∣, where c is the transaction cost. The mathematical programming problem of choosing d₁, ..., d_n to maximize r under a given transaction cost c is shown to have an analytic solution, which is a function of a key summary statistic called the largest change before reversal. The largest change before reversal is recommended to be used as an output in a neural network for the generation of trading signals. When neural network forecasting is applied to a dataset of Hang Seng Index Futures Contract traded in Hong Kong, it is shown that forecasting the largest change before reversal outperforms the k‐step‐ahead forecast in achieving higher trading profits. Copyright © 2000 John Wiley & Sons, Ltd.     

La formule chromosomique chez cinq espèces de Chiroptères

Summary Five species ofChiroptera were studied and the following numbers were found:Rhinolophus hipposideros Bechst.N=27;Barbastella barbastellus Schr.N=16;Plecotus auritus L.N=16;Myotis myotis Bork.N=21;Miniopterus schreibersii Kuhl,N=23. Centric fusions occur in the chromosomal evolution ofChiroptera. Sex-chromosomes ofX-Y type.     

Chemical and tactile communication between the root aphid parasitoidParalipsis enervis and trophobiotic ants: consequences for parasitoid survival

Females of the aphid parasitoidParalipsis enervis received liquid food by regurgitation (trophallaxis) from workers of the ant speciesLasius niger, but were not fed by workers ofMyrmica laevinodis andTetramorium caespitum. WhileP. enervis was not treated aggressively by workers of any of these species,Lasius flavus workers killed the parasitoid. This different ant behaviour resulted in a different parasitoid longevity. WhileP. enervis survived for only 10 min in the presence ofL. flavus (due to ant aggression) or for approximately one day in the presence ofT. caespitum andM. laevinodis (due to lack of trophallaxis), survival increased significantly to more than five days in the presence ofL. niger, which provided food regularly to the parasitoids. Our study suggests thatP. enervis mimics behavioural signals ofL. niger, as well as odor cues of its host aphidAnoecia corni, to avoid aggression byL. niger.     

Dominance for enzyme activity inDrosophila melanogaster

Summary A regulatory element tightly linked to theGpdh locus inDrosophila melanogaster has been isolated from a natural population. Flies homozygous for second chromosomes bearing the element,H31, have half the GPDH activity of normal homozygotes. Heterozygotes betweenH31 andF orS alleles exhibit dominance in GPDH activity. Heterozygotes betweenH31, F orS andDf(2L) GdhA have half the diploid level. The contribution of theS allele to the activity inS/H31 heterozygotes is more than four times that ofH31. The regulatory element distinguishingH31 is tightly linked to theGpdh ⁺ locus.     

Differenzierendes Kaulquappen-Fressen durch Molche

Summary Differential predation on tadpoles by newts (Triturus). 4 EuropeanTriturus species (T. alpestris, T. cristatus, T. helveticus, T. vulgaris) feed upon the tadpoles of the following Anura species which occur in sympatry with the newts:Rana esculenta, R. temporaria andBombina variegata. OnlyTriturus cristatus prey also upon the tadpoles ofBufo bufo andB. calamita. Triturus alpestris, T. helveticus andT. vulgaris do not eat anyBufo tadpoles. Even larvae ofTriturus alpestris prey upon tadpoles ofRana esculenta, R. ridibunda andBombina variegata but avoid tadpoles ofBufo calamita.

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Mit Unterstützung des Schweizerischen Nationalfonds zur Förderung der wissenschaftlichen Forschung.     

On the usefulness of macroeconomic forecasts as inputs to forecasting models

A forecasting model for y_t based on its relationship to exogenous variables (e.g. x?_t) must use x?_t, the forecast of x?_t. An example is given where commercially available x?_t's are sufficiently inaccurate that a univariate model for y_t appears preferable. For a variety of types of models inclusion of an exogenous variable x?_t is shown to worsen the y_t forecasts whenever x?_t must itself be forecast by x?_t and MSE (x?_t) > Var (x?_t). Tests with forecasts from a variety of sources indicate that, with a few notable exceptions, MSE (x?_t) > Var (x?_t) is common for macroeconomic forecasts more than a quarter or two ahead. Thus, either:

• (a) available medium range forecasts for many macroeconomic variables (e.g. the GNP growth rate) are not an improvement over the sample mean (so that such variables are not useful explanatory variables in forecasting models), and/or
• (b) the suboptimization involved in directly replacing x?_t by x?_t is a luxury that we cannot afford.

     

Zur Stratigraphie der säugetierführenden Schichten von Java

Summary According to recent geological and paleontological investigations thePithecanthropus-beds of Java are pleistocene in age. The examinations of the fossil mammalian faunæ of the island are of utmost importance for this age-determination and the following faunæ can be recognized:Tji Djolang-fauna: Middle Pliocene.Kali Glagah-fauna: Upper Pliocene.Djetis-fauna withPithecanthropus: Lower Pleistocene.Trinil-fauna withPithecanthropus: Middle Pleistocene.Ngandong-fauna withHomo neanderthalensis soloensis: Upper Pleistocene.Sampoeng-fauna with a primitive type of the Wedda-Dravida-Australoid group: Subrecent. — Micropaleontological examinations of smallerForaminifera from marine equivalents of thePithecanthropus-beds confirm the age-determinations based on mammalia. — Recent field investigations prove that the lower and middle pleistocenePithecanthropus-beds are distinctlyfolded by a post-middle-pleistocene movement; the upper pleistocene Ngandong-terraces are not folded at all.     

Simple integrated rate equations for reversible bimolecular reactions

Summary If the complete rate equations for reversible, one-step, bimolecular reactions are written withP _e–P as the concentration variable (whereP _e is the equilibrium, andP is the instantaneous, product concentration), the 3 possible stoichiometries can be reduced to a single straightforward differential equation. This can be solved very economically. For each stoichiometry, weret is time,k ₁ is the forward rate constant,K _e is the equilibrium constant, and P isP–P _o. The termsP _c–P _o andD+P _c–P _o are the physically possible and physically impossible roots of the quadratic equation forP _e–P _o in terms of the initial concentrations andK _c.D is the discriminant in this equation. All 3 quantities can be calculated if the equilibrium constant is known. A plot oft against ln{[1–P/(D+P _c–P _o)]/[1–P/(P _c–P _o)]} should be a straight line for any second order reaction. For each stoichiometry,P _c–P _o approachesA _o, the initial concentration of the first reactant, as the equilibrium constant increases. When a second reactant is present,D+P _e–P _o approachesB _o. The limiting equation is then that of an irreversible bimolecular reaction. For AP+Q,D approaches –K _e as the equilibrium constant becomes large, and the value of the second logarithmic term in the integrated equation approaches zero. The limiting equation is that of an irreversible, unimolecular reaction.Acknowledgments. I thank Dr. Athel Cornish-Bowden for many helpful discussions. This work was partially supported by a grant from Utah State University.     

Lens regeneration from cornea in tail ectopic eyes of Xenopus laevis tadpoles

Summary Evidence was found that cornea in tail ectopic eyes of Xenopus tadpoles has the capacity to regenerate a new lens.Supported by an award from the Science Research Council.     

Unstable genetic system inDrosophila melanogaster: I. Instability at theCinnabar locus

Summary A mutant strain containing acinnabar allele (cn ^rbr ,rojo brillante) is reported, that produces wild-type revertants at thecinnabar (cn) locus. Incn ^rbr /cn heterozygotes the rate of mutation is highly increased. The presence of a mutator agent acting premeiotically is indicated.D.L. Lindsley and E.H. Grell, Genetic variations ofDrosophila melanogaster. Carnegie Institution of Washington, Washington, 1968; Publication No. 627.     

Explaining Leibniz equivalence as difference of non-inertial appearances: Dis-solution of the Hole Argument and physical individuation of point-events

“The last remnant of physical objectivity of space–time” is disclosed in the case of a continuous family of spatially non-compact models of general relativity (GR). The physical individuation of point-events is furnished by the autonomous degrees of freedom of the gravitational field (viz., the Dirac observables) which represent—as it were—the ontic part of the metric field. The physical role of the epistemic part (viz. the gauge variables) is likewise clarified as embodying the unavoidable non-inertial aspects of GR. At the end the philosophical import of the Hole Argument is substantially weakened and in fact the Argument itself dissolved, while a specific four-dimensional holistic and structuralist view of space–time (called point-structuralism) emerges, including elements common to the tradition of both substantivalism and relationism. The observables of our models undergo real temporal change: this gives new evidence to the fact that statements like the frozen-time character of evolution, as other ontological claims about GR, are model dependent.