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APPENDIX 
into a kind of groove formed by the scales of the abdomen, one cannot 
doubt that the tufts in question are scent-organs, seeing that they possess 
one of the most essential characteristics of these organs, viz. the special 
protection which, during respose, guards against the dissipation of the 
scent. I have, in fact, had the satisfaction of finding a moth whose 
tibiae emitted a peculiar perfume, which, without being strong, was 
yet perfectly perceptible even to us, with an olfactory sense far inferior 
to that of most Lepidoptera. It was one of the larger species of the 
family of the Erebidae, 1 having a wing expanse of 0*19 metre a species 
no one could overlook. In the females of this Erebid, the tibiae of the 
third pair of legs are slender in form, and, as is usual with the Lepidoptera, 
intermediate in thickness between the femora and tarsi (PI. 0, Pig. 10). 
In the males, on the contrary, these tibiae are extremely thick (PI. C, 
Figs. 11 and 12), so that their breadth (4 mm.) equals one-third of the 
length (12 mm.). The outer surface is slightly convex, and on the inner 
there is a longitudinal groove beginning about 3 or 4 mm. from the base, 
and becoming deeper towards the apex of the tibia, as is best seen in 
transverse sections (Fig. 14). The entire inner surface, except the extreme 
tarsal apex and part of the groove, is covered with hairs of 4-6 mm. in 
length, but shortest along the upper margin (Fig. 13). These hairs are 
capable of being erected, forming a kind of very dense brush, and it is in 
the state of erection that their scent can be perceived. 
In the state of repose, the median hairs lie in the longitudinal furrow 
parallel with the axis of the tibia, and are covered by a thick layer of 
the lateral tibial hairs ; these again are covered by the dense hairs on the 
lower edge of the femur, which also are far more developed in the male 
sex. In this manner the lower hairs, and especially those lying in the 
tibial groove, are sufficiently protected by the superimposed marginal 
hairs and those of the femur, against loss by evaporation of any odo¬ 
riferous substance with which they may be impregnated while in a state 
of repose, whereas, on being erected, they exhibit an enormous surface 
which promotes a corresponding evaporation of the scent. It may be noted 
that even Linnaeus gave to one of the species of Erebidae the name of 
Noctua odora , probably in consequence of its strong scent; but whether 
this was peculiar to the males or produced by the tibiae he does not say. 
There are in the same family other species, whose males have the tibiae 
of ordinary form, without the excessive hairiness of the one above- 
mentioned, but furnished instead with a long tuft of hair issuing from 
the inner side of the base. Finally, still other species of Erebidae appear 
to be destitute of any scent-organs on the legs. Certain genera of the 
Hesperidae are also characterized by the tufts borne by the males on their 
posterior tibiae, while the males of the moth genus Herminia (included 
by some entomologists in the Pyralidae , by others, e.g. Speyer, in the 
Noctuinae ) are usually furnished with larger or smaller tufts on their 
1 Erebus and its allies are Noctuidae of the sub-family Noctuinae. —E.B.P. 
