Abstract
The aqueous exudation from the sagittiform sensilla ofDermacentor andersoniStiles larvae and nymphs, when placed in xylene and kerosene, indicates that the sensilla are more permeable than the rest of the cuticle to water. Potassium hydroxide also penetrates preferentially at these sites, reacting with haem pigments to form a pink colour inDermacentorandBoophiluslarvae. These observations, together with the complex structure of the sensilla, suggest that the sensilla are hygroreceptors.