Chloride excretion in the head region of fundulus heteroclitus.

1. The chloride: excreting cell is not limited to the gill epithelium, being found in other regions of the headrespecially the inner surface of the operculum.2. With one exception, the cells appear identical in morphology and in response to Regand-Altmann, Ludford, and alkaline phosphatase techniques. The exception is that the mitochondria are usually more densely packed in the branchial cells.3. In the operculum, the population density of the chloride cells is in positive ratio to the vascularity of the tissue. Such a topographical positioning of the cell is significant to its function of removing chlorides from the circulatory system.