No abstract

During the course of its embryonic development, the European lobster Homarus gammarus LINI~AEUS exhibits progressive increases in content of water (54.0 to 83A%), ash (2.7 to t6.7%), protein (47.4 to 50.9%) and non-protein nitrogen (1.0 to 2.4%), and steady decreases in content of fat (43.8 to 25.4%) and energy (6343 to 5431 cal/g dry organic substance). Cumulative yolk utilization efficiency during the total development is 81.8% for dry weight; the corresponding value for energy is 60A, for protein 75.6 and for fat 47.4%. Energy content of a single egg is t0.49 cal. Of the 4.20 cal expended for metabolic processes of the embryo, only 13.3% energy is drawn from protein oxidation; fat oxidation supplies as much as 87.7% energy, that of carbohydrate only 2.3%. Embryonic development results in a remarkable decrease in net yolk utilization efficiency, which falls from 85.5% in the early developmental stages, to less than 70% in later developmental stages. The mean dry weight of a single egg membrane increases from 38 ~g (2.2% of egg weight) in a freshly laid and attached egg, to 81 ~g in an egg with an almost completely developed embryo. This result supports the earlier observation of C~.v~o (1966) that the formation of the inner chitinous egg membrane occurs after the egg is laid and attached to the serum. Protein seems to be the major constituent of the egg membrane (4049 cal/g dry weight), which has ~he following composition: protein 70.4%, non-protein nitrogen 0A3%, ash 2.83%. Initial permeability of the egg membrane to water (about 6% of the total water requirement is let in) is followed by a period during which the egg membrane is almost impermeable to water (stages I to III); the egg membrane becomes permeable to water again and lets in 85% of the total water requirement (the rest, i.e. 9%, is metabolic water) at a relatively advanced stage of development. These assumed changes in egg membrane permeability appear to be indicative of variations in the egg's osmoconeentration leading to shirtings in net transport of water, l~ates of water and salt uptake during embryonic development are essentially parallel (Fig. 1). The egg membrane remains permeable to salts throughout development; salt intake almost doubles after the egg passes through stage IIL A single egg, weighing 3.7 mg requires 4.9 mg water for successful completion of embryonic development. The imbibition of water by the developing marine demersal egg seems to (1) serve in osmotic hatching; (2) float the hatched larva by means of specific gravity reduction; (3) aid the larva to quickly adjust its body temperature. The simple osmotic hatching mechanism, proposed by previous workers, seems to * Dedicated to Professor P. KOO~r~KUTT~ MENO:~, Montreal, on his 62nd birthday, June 3, 1970. be inadequate to account for the events and timing of the hatching process in the lobster. It is suggested that hatching time is determined not solely by increased internal pressure caused by inflow of water and salts, but also by some unknown internal factor. In ...

No abstract

No abstract