Some time ago Dr. Cobbold sent me a quantity of fluid which he had extracted from about seventy perfectly fresh specimens of the Ascaris megalocephala of the horse, and he requested me to make an analysis of it. I most willingly availed myself of this unusual opportunity of ascertaining the composition of this fluid, the sample procured by Dr. Cobbold being fortunately large enough for the purpose. The analysis of this fluid is interesting as showing that its composition is similar to that of juice of flesh in the higher animals, and consequently that the process of assimilation occurs in these worms much in the same way as in those animals where the organs of digestion and circulation are perfectly developed. It also shows that a fluid similar to that existing in muscular tissue is apparently elaborated by the intestines of the Ascarides, while in the higher animals this fluid is formed from the blood. The fluid was turbid, of a pale yellow colour, and emitted an offensive odour, although not of decomposition.