X. SCENT-SCALES, MALE “ MAEACUJA BUTTERFLIES ” 659 
which are offensive to insect-eating birds and other enemies, and are thus 
protective. Such scents can be at once distinguished by the fact that 
they occur in both sexes alike, and that the insect emits them when in 
danger, as for instance, when it is caught hold of. The Maracuja butter¬ 
flies, among others, possess such a protective scent, and it is very powerful. 
If one takes hold of any species, male or female, there appear at the apex 
of the abdomen yellow glands, differently shaped and situated in the two 
sexes, but in both alike emitting the same objectionable scent. This cir¬ 
cumstance might well raise doubts as to the significance attributed above 
to the scent-scales : it might seem strange that the male should possess, in 
addition to a very strong scent for scaring foes, another extremely weak 
perfume to attract the females. To this we may reply, that at least one 
case is known in which both scents occur, their sources of origin being 
also close together. Didonis biblis , a pretty, medium-sized, black butterfly 
with a broad red band along the margin of the hind-wings, has in both 
sexes, on the dorsal surface of the abdomen, between the fourth and fifth 
segments, a blackish hairy double gland, which is exserted when the 
creature is seized, but the male possesses in addition a white-haired gland 
also double, which stands out in strong contrast against the black abdomen, 
between the fifth and sixth segments, and is never voluntarily exserted by 
the captured butterfly: this is entirely wanting in the female. With care, 
it is possible to press forward alternately the anterior and posterior gland, 
and to assure oneself of the difference between the perfumes. By means 
of this example, the significance attributed above to the scent-scales of the 
male Maracuja butterflies—which can scarcely be contested—loses that 
strangeness which it would possess were it an isolated case. 
