The alar pocket, located on the upper surface of the hind wing of the male monarch butterfly (Danaus p. plexippus) appears to be of a glandular nature, as is indicated by the cells associated with the androconia and as described by authors reviewed in this paper. Two distinct kinds of modified scales are associated with the cells; one (here termed the "patellate scale") has a relatively broad blade and a deeply penetrating stalk while the other (here termed the "poculate scale") is hair-like, fragile, and penetrates the cell membrane for a short distance. The cell of the poculate scale has a chitinous lip that extends above the plane surface forming a cup-like appearance while the patellate scale is associated with a slightly depressed area. In view of the absence of wing scales at the entrance to the lip of the alar pocket of some species of Danaidae, it has been postulated by many authors that this was caused by the insertion of the male hair pencils into the pocket in order to extract the substance emanating from the gland cells. In the present study there was no evidence of scales being removed from the lip of the pocket and hence it is concluded that such does not take place in this species. It is suggested that the poculate scales, being readily dissociated from the cells, may carry the odour to the outside in a manner similar to that of the spherules or "dust" described for Danaus gelippus berenice. Owing to a lack of experimental data, the function of the alar pockets remains ambiguous.