1. The adhesive force acting between the adhesive organs and substratum for a number of aphid species has been studied. In the case of Aphis fabae, the force per foot is about 10 μN. This is much the same on both glass (amphiphilic) and silanized glass (hydrophobic) surfaces. The adhesive force is about 20 times greater than the gravitational force tending to detach each foot of an inverted aphid. 2. The mechanism of adhesion was considered. Direct van der Waals forces and viscous force were shown to be trivial and electrostatic force and muscular force were shown to be improbable. An adhesive force resulting from surface tension at an air-fluid interface was shown to be adequate and likely. 3. Evidence was collected that the working fluid of the adhesive organ has the properties of a dilute aqueous solution of a surfactant. There is a considerable reserve of fluid, presumably in the cuticle of the adhesive organ.

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An earlier suggestion based on light microscopy that haptor "spicules" in the oncomiracidium of the microbothriid monogenean Leptocotyle minor are vestigial marginal hooklets is supported by their ultrastructural features. Each spicule is a solid rod of homogeneous, uniformly electron-dense material and is enclosed within a cell (or cells) (oncoblast?). We confirmed that there are six of these spicules in L. minor.

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