Structure of Scent Organs in Male Danaine Butterflies. 163 



but consist of a fold or pocket of the wing. As the brushes 

 are of a less complicated structure than the scent-pocket, it 

 will be convenient to describe them first. They consist of 

 the usual membranous bag from which arise the hairs of 

 the brush, which in this species are all of one form and 

 strongly chitinised. It is unnecessary to give a photograph 

 of more than one section of the brush. PI. XV, fig. 4, 

 represents the general appearance of any transverse section 

 of that organ, whilst PI. XIX, fig. 23, shows one of the hairs 

 in section as seen under a high power. I am inclined to 

 think that these hairs are pierced by minute pores. At 

 any rate a very thin section shows a number of pale radial 

 lines between the low ridges which longitudinally traverse 

 the surface. Within the hair-wall is a delicate medullary 

 substance pierced by a longitudinal canal of irregular 

 section, and often of very eccentric position. PL XIX, 

 fig. 21, shows a longitudinal surface view of one of 

 these hairs. The structure is very faint, and only visible 

 under a high power, which shows that the fluting or 

 ribbing is not, at least, in the greater part of the hair 

 parallel with the long axis, but takes an undulating 

 course. With regard to the presence of pores in these 

 hairs, it is curious that their existence should be rather 

 strongly suggested in a species in which their utility is 

 least obvious, for the production of a scent-secretion as 

 well as of a dust material appears, as will be seen later, to 

 be amply provided for by the wing-pocket. One other 

 feature remains to be noted. A considerable portion of 

 the interior of the brush-bag, especially towards the open 

 or distal end, is not smooth as in most of the other species 

 examined, but thrown into a great number of minute 

 irregular folds, giving it on a surface view the appearance 

 of being covered by a mass of tiny excrescences. This 

 feature, which is not accompanied by any glandular develop- 

 ment, occurs also in Danaida chrysippiis. So far its signifi- 

 cance is obscure. 



PI. XV, fig. 5, is a photograph of a section of the scent- 

 pocket in T. jpetiverana. It consists of an outer chitinous 

 layer bearing large scales, and morphologically part of the 

 underside of the wing. Next to this is a layer of irregular 

 cells, followed by a second layer, from which arise the small 

 dark scales seen in the photograph. Within the cavity of 

 the pocket masses of thread-like bodies may be seen lying 

 loose. PI. XIX, fig. 19, shows more accurately the structure 



