Mg++-sensitivity of neuromuscular transmission in two crustaceans: correlation with blood Mg++ levels.

Neuromuscular transmission was measured in muscles of spider crabs (Hyas areneus) and lobsters (Homarus americanus). Solutions containing 40 and 10 mM/1 Mg++, which were approximately the same as those measured in the blood of Hyas and Homarus, respectively, were used to soak the preparations prior to testing. In Homarus, neuromuscular transmission was severely depressed by 40 mM Mg++. In spider crabs, neuromuscular transmission was not severely depressed. Although the amount of transmitter released by nerve impulses was reduced, total membrane depolarization during trains of impulses was not reduced because a compensating increase in muscle fiber membrane resistance occurred in Hyas preparations exposed to M Mg++. Hyas, but not Homarus, is physiologically adapted to function at relatively high blood Mg++ concentrations.     

Types and Life Cycles of Centrioles of Flagellates

SUMMARY. Two centrioles, an old one and a new one, are always present in the resting cell. From prophase onward two new ones and two old ones are present. Beginning with the resting stage, five types of centriole life cycles are described and compared with one another: In type 1, both centrioles are elongate; in type 2, the old one is long and the new one, which is short, elongates in prophase; in type 3, both are short, both elongate in prophase, and both, except for their anterior tips, degenerate in late telophase; in type 4, both are long but in prophase their distal ends become free of the rest of the centrioles, these ends migrate to center or posterior end of cell, where, after they produce the achromatic figure and it completes its function in nuclear division, they degenerate; in type 5, both are short and neither elongates at any stage of its life cycle.
New centrioles are produced by the anterior ends of old ones. In their first generation, centrioles produce only extranuclear organelles (flagella, parabasals, axostyles, etc.); in their second and later generations, they produce only the achromatic figure (gametogenesis in Trichonympha and reorganization in Barbulanympha and Rhynchonympha are exceptions to this rule).
The distal ends of centrioles in some types of cycles are surrounded by centrosomes; in others they are not. In one type of centriole life cycle a small central spindle is present in the resting cell in two genera; in the other types this is not the case.     

Indicators of Dematerialization and the Materials Intensity of Use

We review the major empirical analyses of the related concepts of dematerialization and intensity of use. Dematerialization refen to the absolute or relative reduction in the quantity of materials used and/or the quantity of waste generated in the production of a unit of economic output A common indicator is the intensity of material use, which is the quantity of material used per unit of economic output. Our discussion focuses on seven topics: the environmental Kuznets curve for materials, material use and long wave theory material decomposition analysis, statistical, inpuboutput and dynamic models of material use, and analyses of national material use. We examine the measurement of aggregate material use and waste emissions, hypothesis testing, the importance of imports, and forces that countervail dematerialization such as rising affluence and the "rebound effect." We conclude that: our knowledge of the extent of and mechanisms behind the patterns of material use are limited largely to individual materials or very specific industries, and most of those examples are metals; the economy is getting "lighter" but the aggregate economic significance of that trend, if any, is unknown; there is no compelling macroeconomic evidence that the US. economy is "decoupled" from material inputs; and we know even less about the net environmental effects of many changes in materials use. We caution against gross generalizations about material use, particularly the "gut" feeling that technical change, substitution, and a shift t o the "information age" inexorably lead to decreased materials intensity and reduced environmental impact. We end with some suggestions for research that may help answer these important questions.     

Individual recognition of contact calls by pygmy marmosets

Individual recognition by voice has been frequently assumed to be an important phenomenon in the social species. The present study on pygmy marmosets (Cebuella pygmaea) demonstrated that there are distinctive acoustic features in each of two contact calls by which individuals could be distinguished from each other. Individual pygmy marmosets responded differently depending on which type of contact call was given and on the identity of the vocalizing animal. Playbacks of individual calls through hidden speakers produced some evidence for differential individual responses, but only when they originated from familiar locations. These results indicate that pygmy marmosets recognize each other on the basis of their contact calls.