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EMISSION OF SCENT BY A DELTOID MOTH.
By Prof. RAPHAEL MELDOLA, F.R.S., F.E.S. (Vice-President of the Essex Field Club).
The possession of distinct structures for the secretion and diffusion
of scent by Lepidoptera was first pointed out by Fritz Muller in the
case of certain South American butterflies. Ten years ago I had the
privilege of making known the results of his observations at a meeting
of the Entomological Society of London (Trans. Ent. Soc, 1878,
page 211 ; also Proc. Ent. Soc, 1878, pp. 2 and 27). The wing-
pouches, talc spots, fan-like tufts, etc., found in many Lepidopterous
insects perform the functions referred to ; and, with reference to the
secretion of odoriferous products by these insects, it must be borne in
mind that two distinct purposes may be served, viz., the production
of a nauseous smell to act as a signal of distastefulness, or the
emission of a fragrant odour to serve as a sexual attraction. In the
first case the odour is of the same use as gaudy coloration, and in
the second case it is analogous to that emitted by the males of certain
animals during the breeding season. It is obvious that scent-organs
which perform this second function are of the nature of secondary
sexual characters (in the Darwinian sense), and it is accordingly
observed that they are usually possessed by the male only, and when
present in both sexes are very generally more fully developed in the
male than in the female. The differences between the structure and
functions of the two kinds of organs and the odours emitted by them
have been fully described by Fritz Muller in his various papers on
the subject, and there is no occasion to recapitulate them here.
In the notes to my translation of Weismann's "Studies in the
Theory of Descent" (vol. i., page 103), I called attention to the well-
known presence of fan-like tufts in certain British moths, and
suggested that they were also scent-organs. One of the species
mentioned, the common Herminia tarsipennalis, takes its name from
the possession of such fans on the front legs, the fact that these
structures are present in the male only being strongly suggestive of
the view that they are secondary sexual characters. This suggestion
which I made in the work referred to I am now enabled to confirm
by a direct observation made yesterday (July 19th, 1888) in Epping
Forest.
I had caught and bottled a specimen of this moth, and when
apparently dead had removed it from the cyanide bottle and pinned
it into a box. On opening the latter some time afterwards the insect