The Permeability of the Shell of the Egg of Teleogryllus Commodus Measured with the Aid of Tritiated Water

The eggs of Teleogrylhis commodus, like those of many other species of insects, absorb water during their development. The water enters through the shell at a specific stage in the egg's development, and there is an as yet unresolved problem as to how the control of the flow of water is effected (Browning, 1967). Recently it has been shown that the isolated egg-shell of Locusta migratoria migratorioides is permeable to water at all stages in the egg's development, and the same is probably true of T. commodus (Browning, 1968.) The objections raised by McFarlane (1966) to earlier work by Browning & Forrest (1960), using deuterated water to assess permeability, are therefore probably not valid. Nevertheless Browning & Forrest (i960), for technical reasons, were unable to separate the water held in the shell from that which had penetrated to the yolk and embryo, and as McFarlane (1966) has pointed out, this limits the conclusions that can be drawn from their work. The present experiment, using tritiated water, which can be detected in much lower concentrations than was possible with deuterated water and the equipment then available, aims to obtain information on the following points: (1) the relative permeability of the shell at times when little or no net flow of water is occurring, compared with the permeability during the period of rapid water uptake; (2) the effect of the metabolic rate of the egg on permeability; and (3) the relative quantities of water entering the shell and entering the contents of the egg (using the word 'contents' to include the embryo, embryonic fluids and the yolk).