No abstract

JUST over 50 years ago Heinroth (1922) published the first extensive list of egg weights and adult body weights for 427 species of birds. Since then additional data have appeared and the most extensive list can now be found in SchSnwetter's (1960-72) monumental description of bird eggs. With these as a major backlog, and data for the Fringillidae (Areadon 1943); the Sphenisciformes, Anseriformes, and Procellariiformes (Lack 1968); and Falconiformes (Mebs 1964), more than 800 egg weightbody weight correlates are now available. Our endeavor has been to describe the relationship between egg weight and body weight in mathematical terms that are amenable to further refinements when additional data became available. We have not been concerned with explaining the relationship as Lack (1968) has done in his elegant analysis, but have rather attempted to find out what common principles might emerge from this particular relationship. Our analytical approach is basically the same as suggested originally by Huxley (1923-24), namely to plot log (egg weight) against log (body weight) and to derive a regression equation that expresses egg weight, W, as a function of body weight, B, raised to a power: W : aB ø. The additional data now available allow one to obtain individual regression equat•ens for many orders and families. As Amadon (1943) had anticipated in his review of Huxley's analysis and as Lack (1968) has recently shown for many orders and families, each group of related birds has its characteristic proportionality constant, a. On the other hand, our analysis indicates that the power, b, is most likely the same for all groups, namely 0.675. In addition, the relation of incubation time to body weight is derived (Rahn and Ar 1974); incubation time is shown to be proportional to body weight raised to the 0.166 power. Thus a 10-fold increase in body weight is in general associated-with a 4.73-fold increase in egg weight and a 1.47-fold increase in incubation time. ME•tIODS or ANALYSIS For each order, and in the case of Passeriformes for each family, the paired values of egg weight and body weight were converted to common logarithms, and the regression of log egg weight on log female weight was derived by linear least-squares analysis. In the ordinary method of least squares, it is assumed that the independent variable (here log B) is not subject either to biological variation or to errors of measurement. The residual scatter of the points around the regression line is therefore ascribed entirely to deviations of the dependent variable (here log W) from the 750 The Auk 92: 750-765. October 1975

In a series of recent works, attention has been paid to the functional properties of the avian eggshell: water vapor and respiratory gas conductances, water loss, metabolic rate and incubation time-all these major physiological characteristics of eggs may be closely and intimately related to egg mass, which, in turn, is allometrically related to eggshell structural properties such as thickness, porosity, mass, density and surface area (Wangensteen 1972, Ar et al. 1974, Rahn and Ar 1974, Paganelli et al. 1974, Rahn et al. 1974, Ar and Rahn 1978). These structural and functional relations of bird eggs reveal some variables of importance to the physiology of the embryo, including the gradient in water vapor pressure between egg and nest, the fractional water loss constant, the constancy of gas composition in the air cell, and total oxygen consumption per gram egg during incubation. The ability to hatch successfully is the outcome of a delicate equilibrium among several factors, some of which are inherited in the structure and function of the egg itself, while others are either imposed on the egg by the environment or controlled by the incubating parents.

Handbuch der Oologie, Diego, California, for sending us eggs of the Emu,

The flow method of reaction rate measurement has been adapted to the determination of the rate of diffusion of water into the human red cell. In seven experiments the half-time for diffusion exchange has been found to be 4.2 4-1.1 reset., which is equivalent to a diffusion flow of 8.6 × 10 -9 ml. H20/(see., red cell). This figure has been compared with the rate of water entrance under an osmotic pressure gradient, and has been found to be smaller by a factor of 2.5. The difference between these two rates of water entrance has been interpreted as indicating the presence of water-filled channels in the membrane. An estimate of the equivalent radius of these channels (on the assumption of uniform right cylindrical pores) leads to a value of 3.5 ,~., which is viewed as an operational description of the resistance offered by the membrane to the passage of water.The present experiments were undertaken to measure the in vitro exchange rate of water across the human red cell membrane under isotonic conditions, using tritiated water (THO) as a tracer. To determine the time course of this rapid exchange, a flow method was devised, based on the principles developed by Hartridge and Roughton (1), Dirken and Mook (2), and Chance (3). Freshly drawn, heparinized, whole blood or fresh red cell suspensions were mixed with an isotonic red cell buffer containing THO, and the rate of uptake of the T H O by the cells was followed. The rates of entrance of water by diffusion and by osmosis were then used to calculate an equivalent pore size for the red cell membrane. Experimental MethodPrinciples. m A suspension of ceils and tritiated, isotonic buffer is mixed and forced down an observation tube. As the mixture flows down the tube, the non-labelled intracellular