1. The localization of vitamin C in Nyctotherus cordiformis, Toxocara canis and Opisthioglyphe ranae was investigated by means of the silver nitrateacetic acid technique.
2. In Nyctotherus, the vitamin C is distributed uniformly throughout the cytoplasm in the form of globules of varying sizes. No vitamin is present in the ectoplasmic layer or in the region of the nuclei. In the same preparations specimens of Opalina show no trace of any vitamin C present.
3. In Toxocara, the vitamin is localized in relatively large quantities in all the cells of the intestine. In these cells it is aggregated mainly in the region between the nucleus and the free cell border. A series of fine granules of the vitamin also line the lower cell walls. Only a few scattered granules are present in the remaining tissues.
4. In Opisthioglyphe, the vitamin is concentrated on the walls of the excretory system which in this trematode has the form of two longitudinal canals joining in the posterior region to form a single median canal. A line of disk-like elements of the vitamin is also present immediately below the epidermis. In the remaining tissues only very small scattered grains are found.
5. It is believed that in the case of Toxocara, the presence of the vitamin in the gut cells may indicate that the parasite is capable of absorption of vitamin C from the food of the host.
6. It is suggested that in heavy parasitic infections the parasites may play some part in the disturbance of the vitamin C balance of the host.