APPENDIX. 
* 5 * 
Scent-sacs and Androconia. 
The scent-sacs of Danais limniacce and D. septentrionis (where these appendages 
develop into a deep, narrow pocket or sac on the underside of the hindwing, the opening into the 
sac being on the upperside in the middle of one of the interspaces) contain a few small bundles or. 
packets of grayish-white fibres, which are loose or unattached to the sac ; these fibres break to 
pieces at a touch and soon become dust. The androconia, or long silky hairs in the anal fold of 
the hindwings of some Papilio males have also at their base some of (apparently) the same fibres, 
but I fail to find any in the discal patch of hairs on the upperside of the hindwing of Baoris 
oceia $. The of Discophora tullia has a discal patch of peculiar hairs or scales on the upper- 
side of the hind wing, apparently analagous to that of the “ brands ” in the forewings of many males 
of Euploea. The scent-sacs, as already noted, are supposed to act as allurements to the $ ; Sharp 
says the functions of the androconia are still obscure ; they are believed to exhale scent. The 
scent-sac of Danais septentrionis is formed by an outgrowth of both upper and lower membranes 
of the hindwing, but there seems to be no space between 
the two walls. The interior of the sac is lined with 
specialised scales. The annexed sketch represents a trans¬ 
verse section through the sac, and is diagrammatic and 
much enlarged, the two membranes being shown as if they 
were slightly separated. UM upper membrane. LM lower membrane. OS ordinary wing scales. 
SS specialised scales. NN nervules. 
The scent-sac of D. limniacce is very similar. 
The scent-sac of Danais chrysippus is formed by an outgrowth of the upper wing- 
membrane of the hindwing, and a slight depression of the lower membrane, which form two walls 
with a space between, filled with an oily liquid. The exterior of the sac is covered with the ordinary 
wing-scales, but the interior is lined with minute, peculiar and pale ochreous scales, with a patch 
bare of scales just under the lip of the sac-cover. The annexed diagram represents a transverse 
section (very much enlarged and diagrammatic) through 
the scent-sac:—UM upper membrane, LM lower 
membrane. S interior of sac. O space between the 
membranes filled with liquid. BP space bare of scales. 
N nervule. 
Scent-sac of D. chrysippus. 
The scent-sac of D. plexippus is very similar. 
