( xcv ) 



function of specialised cells embedded in the hypodermis of 

 the wing. Cells of this kind, noticed by Weismann in 1878, 

 have been described and figured by Giinther under the name 

 of " Driisenzelle " or " gland-cells," though so far as I am 

 aware they have not yet been observed in direct connection 

 with the plume-scales. The odoriferous seci-etion, which is 

 possibly of the nature of a volatile oil, must pass in the first 

 instance into the basal disc ; thence along the footstalk, which 

 is undoubtedly tubular, into the interior of the lamina or 

 main portion of the scale ; and finally into the outer air by 

 way of the array of fimbriae. 



The basal appendage, by which the whole scale articulates 

 with its socket in the membrane of the wing, has by some 

 writers been called the "bulb." But it is certainly in most 

 cases a comparatively fl^at structure like the lamina itself, and 

 I therefore prefer to speak of it as the basal or accessory 

 *' disc," or simply as the " disc " without qualification. It is 

 usually furnished with an internal chitinous structure which 

 in many cases bears the appearance of a convoluted tube. 

 There is also apparent in many instances an aperture, gener- 

 ally proximal, by which I suppose the interior of the disc 

 to be put into communication with the secretory apparatus 

 contained in the wing. Connection between the interior of 

 the disc and that of the lamina is provided by means of the 

 pervious footstalk. 



The footstalk often shows a sharp S-shaped bend ; but it 

 may, at least in the detached scale, be straight. The portion 

 of the basal area of the lamina immediately adjacent to the 

 insertion of the footstalk is usually clear ; and, except for a 

 fan-shaped system of faintly-marked streaks radiating from 

 the point of insertion, is apparently structureless ; but at a 

 distance from that point, which varies according to the species, 

 a chitinous structure becomes visible. This occupies the in- 

 terior of the lamina, and frequently presents a more or less 

 scalariform appearance. A longer or shorter region at the 

 distal end of the lamina is again comparatively clear, often 

 exhibiting a longitudinal sti-iation, which may be faint or 

 distinct. It frequently happens that between this striated 

 area and the portion of the lamina exhibiting the scalariform 



