ABSTRACT
Vialli (1923, see Schopfer, 1927), Duval & Courtois (1928) and Schopfer (1924, 1925, 1926, 1927, 1932) have shown by means of freezing-point determinations that the osmotic pressure of the body fluid of Parascaris megalocephala and Ascaris vitulorum is lower than that of their hosts. Schopfer (1932) found that the depression of the freezing point of extracts of whole specimens of A. ovis and A. lumbricoides was in each case less than that of the intestinal fluid of the host. He (1932) also found a similar relationship in the case of Proleptus obtusus, an intestinal parasite of Scyliorhinus caniculus, and Panikkar & Sproston (1941) came to the same conclusion as the result of their work on an unidentified species of Angusticaecum from the tortoise. In free-living land or fresh-water nematodes the body fluid is presumably hypertonic to the environment, and Stephenson’s work (1942) indicates that in Rhabditis terrestris this is, in fact, the case, and that there is an active process of osmotic regulation by means of which this difference in osmotic pressure is maintained.
