[en] 1. The chemical composition of the blood and of the intracellular medium of the muscles has been studied in the king crab (Limulus polyphemus) and compared with that of marine decapods (Crustaceans) and of a scorpion, Androctonus australis. 2. The blood of Limulus contains only very small amounts of free amino acids. The amino-acid composition of the muscles of Limulus differs from that of decapods, but is similar to that of the scorpion, with respect to its lower concentration and to the relative proportions of free arginine and free glycine. 3. The intracellular osmolar effectors in Limulus are principally dialysable nitrogenous compounds, other than amino acids and taurine. These unidentified substances play an important role in the isosmotic intracellular regulation which takes place when Limulus is adapted to brackish water (40 % sea water). This is another difference between Limulus and marine decapods ; the latter show a regulation in which free amino acids are among the most important effectors.
